Bring skydebugger closer to clean-shutdown

This teaches the SkyDebugger prompt how to tell
the sky debugger (server) to shut down instead of
just calling exit(0).

This also teaches the WindowManagerApp (server) how
to tear down all of its connections itself instead
of depending on the pipes to do so (which would
crash when youd delete the WindowManagerApp as the
pipes could outlive it with WindowManagerImpl objects
containing raw pointers back to the WindowManagerApp).

Shutdown is not yet clean.  It errors out trying to
talk to the X11 server, but it's closer to clean
than it was prior to this change.  I may add back
and exit(0) to side-step shutdown until it can be
made fully clean.

R=jamesr@chromium.org, sky@chromium.org
BUG=430291, 430242

Review URL: https://codereview.chromium.org/695183003

engine/src/flutter/tools/debugger/debugger.cc

@@ -66,13 +66,11 @@ void SkyDebugger::OnEmbed(
 }
 
 void SkyDebugger::OnViewManagerDisconnected(mojo::ViewManager* view_manager) {
-  CHECK(false); // FIXME: This is dead code, why?
   view_manager_ = nullptr;
   root_ = nullptr;
 }
 
 void SkyDebugger::OnViewDestroyed(mojo::View* view) {
-  CHECK(false); // FIXME: This is dead code, why?
   view->RemoveObserver(this);
 }
 
@@ -101,6 +99,16 @@ void SkyDebugger::NavigateToURL(const mojo::String& url) {
   }
 }
 
+void SkyDebugger::Shutdown() {
+  // Make sure we shut down mojo before quitting the message loop or things
+  // like blink::shutdown() may try to talk to the message loop and crash.
+  window_manager_app_.reset();
+
+  // TODO(eseidel): This still hits an X11 error which I don't understand
+  // "X Error of failed request:  GLXBadDrawable", crbug.com/430581
+  mojo::ApplicationImpl::Terminate();
+}
+
 void SkyDebugger::InjectInspector() {
   InspectorServicePtr inspector_service;
   mojo::ConnectToService(viewer_services_.get(), &inspector_service);

engine/src/flutter/tools/debugger/debugger.h

@@ -36,6 +36,7 @@ class SkyDebugger : public mojo::ApplicationDelegate,
   // Overridden from Debugger
   void NavigateToURL(const mojo::String& url) override;
   void InjectInspector() override;
+  void Shutdown() override;
 
  private:
   // Overridden from mojo::ApplicationDelegate:

engine/src/flutter/tools/debugger/debugger.mojom

@@ -7,4 +7,5 @@ module sky;
 interface Debugger {
   NavigateToURL(string url);
   InjectInspector();
+  Shutdown();
 };

engine/src/flutter/tools/debugger/prompt/prompt.cc

@@ -132,7 +132,7 @@ class Prompt : public mojo::ApplicationDelegate {
 
   void Quit() {
     std::cout << "quitting" << std::endl;
-    exit(0);
+    debugger_->Shutdown();
   }
 
   void ToggleTracing() {