cc: Make animations tick regardless of drawing.

cc/trees/single_thread_proxy.h

Index: cc/trees/single_thread_proxy.h
diff --git a/cc/trees/single_thread_proxy.h b/cc/trees/single_thread_proxy.h
index 140ef208eb0b011d7cfc363cb5e77b4932c91d23..13756204434bfa984536dea31d195649fb0694be 100644
--- a/cc/trees/single_thread_proxy.h
+++ b/cc/trees/single_thread_proxy.h
@@ -53,7 +53,7 @@ class SingleThreadProxy : public Proxy, LayerTreeHostImplClient {
   virtual void OnVSyncParametersChanged(base::TimeTicks timebase,
                                         base::TimeDelta interval) OVERRIDE {}
   virtual void DidVSync(base::TimeTicks frame_time) OVERRIDE {}
-  virtual void OnCanDrawStateChanged(bool can_draw) OVERRIDE {}
+  virtual void OnCanDrawStateChanged(bool can_draw) OVERRIDE;
   virtual void OnHasPendingTreeStateChanged(bool have_pending_tree) OVERRIDE;
   virtual void SetNeedsRedrawOnImplThread() OVERRIDE;
   virtual void DidInitializeVisibleTileOnImplThread() OVERRIDE;
@@ -85,6 +85,8 @@ class SingleThreadProxy : public Proxy, LayerTreeHostImplClient {
       base::TimeTicks frame_begin_time);
   void DidSwapFrame();
 
+  bool ShouldComposite() const;
+
   // Accessed on main thread only.
   LayerTreeHost* layer_tree_host_;
   bool output_surface_lost_;