webview: Initialize synchronous compositor after first activation.

content/browser/android/in_process/synchronous_compositor_impl.h

Index: content/browser/android/in_process/synchronous_compositor_impl.h
diff --git a/content/browser/android/in_process/synchronous_compositor_impl.h b/content/browser/android/in_process/synchronous_compositor_impl.h
index 48bdd5b48e7fe1ee60f85bc9bf05c8f3ca698c88..f5529dc7ddf23bb217840abf1c8100450031c953 100644
--- a/content/browser/android/in_process/synchronous_compositor_impl.h
+++ b/content/browser/android/in_process/synchronous_compositor_impl.h
@@ -99,6 +99,7 @@ class SynchronousCompositorImpl
   ~SynchronousCompositorImpl() override;
 
   void SetClient(SynchronousCompositorClient* compositor_client);
+  void RegisterWithClient();
   void UpdateFrameMetaData(const cc::CompositorFrameMetadata& frame_info);
   void DidActivatePendingTree();
   void DeliverMessages();
@@ -112,6 +113,7 @@ class SynchronousCompositorImpl
   WebContents* contents_;
   const int routing_id_;
   cc::InputHandler* input_handler_;
+  bool registered_with_client_;
   bool is_active_;
   bool renderer_needs_begin_frames_;