aura: fix hang when the content window is removed from the tree while a swap is pending

content/browser/renderer_host/render_widget_host_view_aura.cc

Index: content/browser/renderer_host/render_widget_host_view_aura.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_aura.cc b/content/browser/renderer_host/render_widget_host_view_aura.cc
index 71ed801b5540e414c61967f395035ef04c7109a9..6a5c1593d3dd5878f88b3287a206ffda1b10a6c9 100644
--- a/content/browser/renderer_host/render_widget_host_view_aura.cc
+++ b/content/browser/renderer_host/render_widget_host_view_aura.cc
@@ -112,10 +112,7 @@ class RenderWidgetHostViewAura::WindowObserver : public aura::WindowObserver {
 
     // Overridden from aura::WindowObserver:
   virtual void OnWindowRemovingFromRootWindow(aura::Window* window) OVERRIDE {
-    // TODO: It would be better to not use aura::RootWindow here
-    ui::Compositor* compositor = view_->GetCompositor();
-    if (compositor && compositor->HasObserver(view_))
-      compositor->RemoveObserver(view_);
+    view_->RemovingFromRootWindow();
   }
 
  private:
@@ -1006,12 +1003,7 @@ void RenderWidgetHostViewAura::OnLostActive() {
 // RenderWidgetHostViewAura, ui::CompositorDelegate implementation:
 
 void RenderWidgetHostViewAura::OnCompositingEnded(ui::Compositor* compositor) {
-  for (std::vector< base::Callback<void(void)> >::const_iterator
-      it = on_compositing_ended_callbacks_.begin();
-      it != on_compositing_ended_callbacks_.end(); ++it) {
-    it->Run();
-  }
-  on_compositing_ended_callbacks_.clear();
+  RunCompositingCallbacks();
   compositor->RemoveObserver(this);
 }
 
@@ -1124,6 +1116,28 @@ bool RenderWidgetHostViewAura::ShouldMoveToCenter() {
       global_mouse_position_.y() > rect.bottom() - border_y;
 }
 
+void RenderWidgetHostViewAura::RunCompositingCallbacks() {
+  for (std::vector< base::Callback<void(void)> >::const_iterator
+      it = on_compositing_ended_callbacks_.begin();
+      it != on_compositing_ended_callbacks_.end(); ++it) {
+    it->Run();
+  }
+  on_compositing_ended_callbacks_.clear();
+}
+
+void RenderWidgetHostViewAura::RemovingFromRootWindow() {
+  // We are about to disconnect ourselves from the compositor, we need to issue
+  // the callbacks now, because we won't get notified when the frame is done.
+  // TODO(piman): this might in theory cause a race where the GPU process starts
+  // drawing to the buffer we haven't yet displayed. This will only show for 1
+  // frame though, because we will reissue a new frame right away without that
+  // composited data.
+  RunCompositingCallbacks();
+  ui::Compositor* compositor = GetCompositor();
+  if (compositor && compositor->HasObserver(this))
+    compositor->RemoveObserver(this);
+}
+
 ui::Compositor* RenderWidgetHostViewAura::GetCompositor() {
   aura::RootWindow* root_window = window_->GetRootWindow();
   return root_window ? root_window->compositor() : NULL;