cc: Don't draw and swap if the frame will not change.

cc/trees/layer_tree_host_impl.h

Index: cc/trees/layer_tree_host_impl.h
diff --git a/cc/trees/layer_tree_host_impl.h b/cc/trees/layer_tree_host_impl.h
index e69291d1d3c5c9106244e7a19db2679cd5aa4e42..bb8a47bb3bb582b1e8ca0625cbb481dbc4f0c2f3 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -125,6 +125,7 @@ class CC_EXPORT LayerTreeHostImpl : public InputHandlerClient,
     const LayerList* render_surface_layer_list;
     LayerList will_draw_layers;
     bool contains_incomplete_tile;
+    bool has_no_damage;

[enne (OOO), 2013/03/26 01:42:07]

Weren't you just saying FrameData had too many members?

[danakj, 2013/03/26 02:00:10]

Yes, this is bad and I feel bad.

I tried to do this differently, but you can't just decide based on the
|render_passes| being empty, or on the damage being empty, because these are
always true once you get to SwapBuffers(). So.. yeh.

 
     // RenderPassSink implementation.
     virtual void AppendRenderPass(scoped_ptr<RenderPass> render_pass) OVERRIDE;
@@ -142,7 +143,8 @@ class CC_EXPORT LayerTreeHostImpl : public InputHandlerClient,
   // to avoid displaying the frame. If PrepareToDraw is called, DidDrawAllLayers
   // must also be called, regardless of whether DrawLayers is called between the
   // two.
-  virtual bool PrepareToDraw(FrameData* frame);
+  virtual bool PrepareToDraw(FrameData* frame,
+                             gfx::Rect device_viewport_damage_rect);
   virtual void DrawLayers(FrameData* frame, base::TimeTicks frame_begin_time);
   // Must be called if and only if PrepareToDraw was called.
   void DidDrawAllLayers(const FrameData& frame);
@@ -198,7 +200,7 @@ class CC_EXPORT LayerTreeHostImpl : public InputHandlerClient,
   Renderer* renderer() { return renderer_.get(); }
   const RendererCapabilities& GetRendererCapabilities() const;
 
-  virtual bool SwapBuffers();
+  virtual bool SwapBuffers(const FrameData& frame);
 
   void Readback(void* pixels, gfx::Rect rect_in_device_viewport);
 
@@ -447,13 +449,14 @@ class CC_EXPORT LayerTreeHostImpl : public InputHandlerClient,
   int64 num_main_thread_scrolls_;
 
   int64 cumulative_num_layers_drawn_;
-
   int64 cumulative_num_missing_tiles_;
 
   size_t last_sent_memory_visible_bytes_;
   size_t last_sent_memory_visible_and_nearby_bytes_;
   size_t last_sent_memory_use_bytes_;
 
+  bool next_frame_damages_full_device_viewport_;
+
   base::TimeTicks current_frame_time_;
 
   scoped_ptr<AnimationRegistrar> animation_registrar_;