Turn StyleSharing to 11.

In Sky we can style share if our TreeScopes have the same styles, our :host
styles are the same, and we'd inherit the same styles. This allows a lot of
simplification to the style sharing logic since we don't need to deal with
descendant selectors or tree boundary crossing rules:

- We can remove the logic that was checking that we were distributed
to the same insertion points since there's no ::content selectors.

- We can check the actual inherited values instead of looking at the
parentOrSHadowHostNode(). We used to look at the node in Blink because we
were checking that you'd get the same descendant selectors applied. In Sky
we instead want to make sure you'd inherit the same values. This also
means we don't need the element().parentOrShadowHostElement() != parent case
in the SharedStyleFinder which was trying to deal with descendant selectors
again.

I also removed the checks that were redundant with the checks inside
supportsStyleSharing() which we always check before adding sharing
candidates.

Finally by refactoring the code to make the TreeScope style check work it
exposed that the Document::styleSheets() and TreeScope::styleSheets() APIs
are now dead. A future patch will delete the now dead StyleSheetList class
as well.

This change makes the city-list application share between all the items in
the list, and all of the headers of the same type now share as well.

R=ojan@chromium.org

Review URL: https://codereview.chromium.org/796713002

engine/core/css/resolver/SharedStyleFinder.cpp

@@ -102,60 +102,37 @@ bool SharedStyleFinder::sharingCandidateCanShareHostStyles(Element& candidate) c
     return elementShadow->hasSameStyles(candidateShadow);
 }
 
-bool SharedStyleFinder::sharingCandidateDistributedToSameInsertionPoint(Element& candidate) const
-{
-    Vector<RawPtr<InsertionPoint>, 8> insertionPoints, candidateInsertionPoints;
-    collectDestinationInsertionPoints(element(), insertionPoints);
-    collectDestinationInsertionPoints(candidate, candidateInsertionPoints);
-    if (insertionPoints.size() != candidateInsertionPoints.size())
-        return false;
-    for (size_t i = 0; i < insertionPoints.size(); ++i) {
-        if (insertionPoints[i] != candidateInsertionPoints[i])
-            return false;
-    }
-    return true;
-}
-
 bool SharedStyleFinder::canShareStyleWithElement(Element& candidate) const
 {
+    ASSERT(candidate.supportsStyleSharing());
+
     if (element() == candidate)
         return false;
-    Element* parent = candidate.parentOrShadowHostElement();
+    if (candidate.tagQName() != element().tagQName())
+        return false;
+    if (candidate.needsStyleRecalc())
+        return false;
     RenderStyle* style = candidate.renderStyle();
     if (!style)
         return false;
     if (!style->isSharable())
         return false;
+    ContainerNode* parent = NodeRenderingTraversal::parent(&candidate);
     if (!parent)
         return false;
-    if (element().parentOrShadowHostElement()->renderStyle() != parent->renderStyle())
+    RenderStyle* parentStyle = parent->renderStyle();
+    if (!parentStyle)
         return false;
-    if (candidate.tagQName() != element().tagQName())
-        return false;
-    if (candidate.inlineStyle())
-        return false;
-    if (candidate.needsStyleRecalc())
+    if (m_renderingParent->renderStyle()->inheritedNotEqual(parentStyle))
         return false;
     if (!sharingCandidateHasIdenticalStyleAffectingAttributes(candidate))
         return false;
-    if (candidate.hasID() && m_features.hasSelectorForId(candidate.idForStyleResolution()))
-        return false;
     if (!sharingCandidateCanShareHostStyles(candidate))
         return false;
-    if (!sharingCandidateDistributedToSameInsertionPoint(candidate))
+    if (!candidate.treeScope().hasSameStyles(element().treeScope()))
         return false;
     if (candidate.isUnresolvedCustomElement() != element().isUnresolvedCustomElement())
         return false;
-
-    if (element().parentOrShadowHostElement() != parent) {
-        if (!parent->isStyledElement())
-            return false;
-        if (parent->inlineStyle())
-            return false;
-        if (parent->hasID() && m_features.hasSelectorForId(parent->idForStyleResolution()))
-            return false;
-    }
-
     return true;
 }
 
@@ -200,6 +177,7 @@ RenderStyle* SharedStyleFinder::findSharedStyle()
 
     // Cache whether context.element() is affected by any known class selectors.
     m_elementAffectedByClassRules = element().hasClass() && classNamesAffectedByRules(element());
+    m_renderingParent = NodeRenderingTraversal::parent(&element());
 
     Element* shareElement = findElementForStyleSharing();
 

engine/core/css/resolver/SharedStyleFinder.h

@@ -46,6 +46,7 @@ public:
         , m_features(features)
         , m_styleResolver(styleResolver)
         , m_context(context)
+        , m_renderingParent(nullptr)
     { }
 
     RenderStyle* findSharedStyle();
@@ -71,6 +72,7 @@ private:
     const RuleFeatureSet& m_features;
     StyleResolver& m_styleResolver;
     const ElementResolveContext& m_context;
+    ContainerNode* m_renderingParent;
 };
 
 } // namespace blink

engine/core/css/resolver/StyleResolver.cpp

@@ -261,6 +261,7 @@ void StyleResolver::addToStyleSharingList(Element& element)
     // otherwise we could leave stale pointers in there.
     if (!document().inStyleRecalc())
         return;
+    ASSERT(element.supportsStyleSharing());
     INCREMENT_STYLE_STATS_COUNTER(*this, sharedStyleCandidates);
     StyleSharingList& list = styleSharingList();
     if (list.size() >= styleSharingListSize)

engine/core/dom/Document.cpp

@@ -331,8 +331,6 @@ Document::~Document()
 #endif
 
 #if !ENABLE(OILPAN)
-    if (m_styleSheetList)
-        m_styleSheetList->detachFromDocument();
 
     if (m_importsController)
         HTMLImportsController::removeFrom(*this);
@@ -1677,13 +1675,6 @@ PassRefPtr<Document> Document::cloneDocumentWithoutChildren()
     return create(DocumentInit(url()).withRegistrationContext(registrationContext()));
 }
 
-StyleSheetList* Document::styleSheets()
-{
-    if (!m_styleSheetList)
-        m_styleSheetList = StyleSheetList::create(this);
-    return m_styleSheetList.get();
-}
-
 void Document::evaluateMediaQueryListIfNeeded()
 {
     if (!m_evaluateMediaQueriesOnStyleRecalc)

engine/core/dom/Document.h

@@ -233,9 +233,6 @@ public:
     bool isRenderingReady() const { return haveImportsLoaded(); }
     bool isScriptExecutionReady() const { return isRenderingReady(); }
 
-    // This is a DOM function.
-    StyleSheetList* styleSheets();
-
     StyleEngine* styleEngine() { return m_styleEngine.get(); }
 
     // Called when one or more stylesheets in the document may have been added, removed, or changed.
@@ -719,7 +716,6 @@ private:
     MutationObserverOptions m_mutationObserverTypes;
 
     OwnPtr<StyleEngine> m_styleEngine;
-    RefPtr<StyleSheetList> m_styleSheetList;
 
     TextLinkColors m_textLinkColors;
 

engine/core/dom/Element.cpp

@@ -990,15 +990,8 @@ StyleRecalcChange Element::recalcOwnStyle(StyleRecalcChange change)
     ASSERT(oldStyle);
 
     if (RenderObject* renderer = this->renderer()) {
-        if (localChange != NoChange) {
+        if (localChange != NoChange)
             renderer->setStyle(newStyle.get());
-        } else {
-            // Although no change occurred, we use the new style so that the cousin style sharing code won't get
-            // fooled into believing this style is the same.
-            // FIXME: We may be able to remove this hack, see discussion in
-            // https://codereview.chromium.org/30453002/
-            renderer->setStyleInternal(newStyle.get());
-        }
     }
 
     if (styleChangeType() >= SubtreeStyleChange)

engine/core/dom/TreeScope.cpp

@@ -28,6 +28,7 @@
 #include "sky/engine/core/dom/TreeScope.h"
 
 #include "gen/sky/core/HTMLNames.h"
+#include "sky/engine/core/css/StyleSheetList.h"
 #include "sky/engine/core/css/resolver/ScopedStyleResolver.h"
 #include "sky/engine/core/dom/ContainerNode.h"
 #include "sky/engine/core/dom/Document.h"
@@ -420,4 +421,22 @@ void TreeScope::setNeedsStyleRecalcForViewportUnits()
     }
 }
 
+bool TreeScope::hasSameStyles(TreeScope& other)
+{
+    if (this == &other)
+        return true;
+    const Vector<RefPtr<blink::CSSStyleSheet> >& list = document().styleEngine()->styleSheetsForStyleSheetList(*this);
+    const Vector<RefPtr<blink::CSSStyleSheet> >& otherList = document().styleEngine()->styleSheetsForStyleSheetList(other);
+
+    if (list.size() != otherList.size())
+        return false;
+
+    for (size_t i = 0; i < list.size(); i++) {
+        if (list[i]->contents() != otherList[i]->contents())
+            return false;
+    }
+
+    return true;
+}
+
 } // namespace blink

engine/core/dom/TreeScope.h

@@ -38,8 +38,8 @@ class DOMSelection;
 class Document;
 class Element;
 class HitTestResult;
-class ScopedStyleResolver;
 class Node;
+class ScopedStyleResolver;
 
 // A class which inherits both Node and TreeScope must call clearRareData() in its destructor
 // so that the Node destructor no longer does problematic NodeList cache manipulation in
@@ -77,6 +77,7 @@ public:
 
     ContainerNode& rootNode() const { return *m_rootNode; }
 
+    bool hasSameStyles(TreeScope&);
 
 #if !ENABLE(OILPAN)
     // Nodes belonging to this scope hold guard references -

engine/core/dom/shadow/ElementShadow.cpp

@@ -208,23 +208,11 @@ bool ElementShadow::hasSameStyles(const ElementShadow* other) const
 {
     ShadowRoot* root = m_shadowRoot;
     ShadowRoot* otherRoot = other->shadowRoot();
-    if (root || otherRoot) {
-        if (!root || !otherRoot)
-            return false;
-
-        StyleSheetList* list = root->styleSheets();
-        StyleSheetList* otherList = otherRoot->styleSheets();
-
-        if (list->length() != otherList->length())
-            return false;
-
-        for (size_t i = 0; i < list->length(); i++) {
-            if (list->item(i)->contents() != otherList->item(i)->contents())
-                return false;
-        }
-    }
-
-    return true;
+    if (!root && !otherRoot)
+        return true;
+    if (root && otherRoot)
+        return root->hasSameStyles(*otherRoot);
+    return false;
 }
 
 const InsertionPoint* ElementShadow::finalDestinationInsertionPointFor(const Node* key) const

engine/core/dom/shadow/ShadowRoot.cpp

@@ -58,9 +58,6 @@ ShadowRoot::ShadowRoot(Document& document)
 
 ShadowRoot::~ShadowRoot()
 {
-    if (m_shadowRootRareData && m_shadowRootRareData->styleSheets())
-        m_shadowRootRareData->styleSheets()->detachFromDocument();
-
     document().styleEngine()->didRemoveShadowRoot(this);
 
     // We cannot let ContainerNode destructor call willBeDeletedFromDocument()
@@ -235,12 +232,4 @@ const Vector<RefPtr<InsertionPoint> >& ShadowRoot::descendantInsertionPoints()
     return m_shadowRootRareData->descendantInsertionPoints();
 }
 
-StyleSheetList* ShadowRoot::styleSheets()
-{
-    if (!ensureShadowRootRareData()->styleSheets())
-        m_shadowRootRareData->setStyleSheets(StyleSheetList::create(this));
-
-    return m_shadowRootRareData->styleSheets();
-}
-
 }

engine/core/dom/shadow/ShadowRoot.h

@@ -87,8 +87,6 @@ public:
     PassRefPtr<Node> cloneNode(bool, ExceptionState&);
     PassRefPtr<Node> cloneNode(ExceptionState& exceptionState) { return cloneNode(true, exceptionState); }
 
-    StyleSheetList* styleSheets();
-
 private:
     ShadowRoot(Document&);
     virtual ~ShadowRoot();

engine/core/dom/shadow/ShadowRootRareData.h

@@ -60,15 +60,10 @@ public:
     void setDescendantInsertionPoints(Vector<RefPtr<InsertionPoint> >& list) { m_descendantInsertionPoints.swap(list); }
     void clearDescendantInsertionPoints() { m_descendantInsertionPoints.clear(); }
 
-    StyleSheetList* styleSheets() { return m_styleSheetList.get(); }
-    void setStyleSheets(PassRefPtr<StyleSheetList> styleSheetList) { m_styleSheetList = styleSheetList; }
-
-
 private:
     unsigned m_descendantContentElementCount;
     unsigned m_childShadowRootCount;
     Vector<RefPtr<InsertionPoint> > m_descendantInsertionPoints;
-    RefPtr<StyleSheetList> m_styleSheetList;
 };
 
 inline void ShadowRootRareData::didAddInsertionPoint(InsertionPoint* point)