Add ParagraphBuilder::PeekStyle() to allow Flutter style inheritance.

Change-Id: Ia198778d9a7cfd7053390e6195bf8e03245add77

src/paragraph.h

@@ -52,7 +52,7 @@ class Paragraph {
 
   ~Paragraph();
 
-  // NOTE: Minikin Layout doLayout() and LineBreaker addStyleRun() has an
+  // Minikin Layout doLayout() and LineBreaker addStyleRun() has an
   // O(N^2) (according to benchmarks) time complexity where N is the total
   // number of characters. However, this is not significant for reasonably sized
   // paragraphs. It is currently recommended to break up very long paragraphs

src/paragraph_builder.cc

@@ -72,6 +72,10 @@ void ParagraphBuilder::Pop() {
   runs_.StartRun(style_index, text_index);
 }
 
+const TextStyle& ParagraphBuilder::PeekStyle() const {
+  return runs_.PeekStyle();
+}
+
 void ParagraphBuilder::AddText(const std::u16string& text) {
   text_.insert(text_.end(), text.begin(), text.end());
 }

src/paragraph_builder.h

@@ -56,6 +56,9 @@ class ParagraphBuilder {
   //   builder.AddText(" Back to normal again.");
   void Pop();
 
+  // Returns the last TextStyle on the stack.
+  const TextStyle& PeekStyle() const;
+
   // Adds text to the builder. Forms the proper runs to use the upper-most style
   // on the style_stack_;
   void AddText(const std::u16string& text);

src/styled_runs.cc

@@ -46,6 +46,10 @@ size_t StyledRuns::AddStyle(const TextStyle& style) {
   return style_index;
 }
 
+const TextStyle& StyledRuns::PeekStyle() const {
+  return styles_.back();
+}
+
 void StyledRuns::StartRun(size_t style_index, size_t start) {
   runs_.push_back(IndexedRun{style_index, start, start});
 }

src/styled_runs.h

@@ -49,6 +49,9 @@ class StyledRuns {
 
   size_t AddStyle(const TextStyle& style);
 
+  // Returns the last TextStyle on the stack.
+  const TextStyle& PeekStyle() const;
+
   void StartRun(size_t style_index, size_t start);
 
   void EndRunIfNeeded(size_t end);