cc: Make scheduling be driven by vsync for android webview.

cc/output/output_surface.h

Index: cc/output/output_surface.h
diff --git a/cc/output/output_surface.h b/cc/output/output_surface.h
index e0b13ece972c7e772ecd2f69a366635ed650b6a7..43cf7a4b56afd6d8759a596cce44a86d501b50ca 100644
--- a/cc/output/output_surface.h
+++ b/cc/output/output_surface.h
@@ -151,6 +151,12 @@ class CC_EXPORT OutputSurface {
   void DidLoseOutputSurface();
   void SetMemoryPolicy(const ManagedMemoryPolicy& policy);
 
+  // Support for a pull-model where draws are requested by the output surface.
+  //
+  // OutputSurface::Invalidate is called by the compositor to notify that
+  // there's new content.
+  virtual void Invalidate() {}
+
  protected:
   OutputSurfaceClient* client_;