Display skips swapping if overlays draw the damage

cc/output/renderer.h

Index: cc/output/renderer.h
diff --git a/cc/output/renderer.h b/cc/output/renderer.h
index 82b3ae307c0b1712455b2935845a04c34db91f8a..0893d67fc60962540c272ee6277706c1faa946ac 100644
--- a/cc/output/renderer.h
+++ b/cc/output/renderer.h
@@ -22,6 +22,12 @@ class Task;
 
 typedef std::vector<scoped_ptr<RenderPass>> RenderPassList;
 
+enum class DrawFrameResult {
+  DID_DRAW,
+  // No drawing was done because overlay planes accounted for the damage.
+  DAMAGE_DRAWN_BY_OVERLAYS,
+};
+
 struct RendererCapabilitiesImpl {
   RendererCapabilitiesImpl();
   ~RendererCapabilitiesImpl();
@@ -63,11 +69,12 @@ class CC_EXPORT Renderer {
   // to frame and should not be cached.
   // The |device_viewport_rect| and |device_clip_rect| are in non-y-flipped
   // window space.
-  virtual void DrawFrame(RenderPassList* render_passes_in_draw_order,
-                         float device_scale_factor,
-                         const gfx::Rect& device_viewport_rect,
-                         const gfx::Rect& device_clip_rect,
-                         bool disable_picture_quad_image_filtering) = 0;
+  virtual DrawFrameResult DrawFrame(
+      RenderPassList* render_passes_in_draw_order,
+      float device_scale_factor,
+      const gfx::Rect& device_viewport_rect,
+      const gfx::Rect& device_clip_rect,
+      bool disable_picture_quad_image_filtering) = 0;
 
   // Waits for rendering to finish.
   virtual void Finish() = 0;