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 3e3b085dcff57109232fbceaa78c11a3b57cf2dd..b72f7fd5571dbe634a330f7788504b5abc9bfffb 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_;