blimp: Use SwapPromises for readback API.

blimp/client/core/render_widget/blimp_document_manager.h

Index: blimp/client/core/render_widget/blimp_document_manager.h
diff --git a/blimp/client/core/render_widget/blimp_document_manager.h b/blimp/client/core/render_widget/blimp_document_manager.h
index 10b1afb72b444670186bd0d91f38fd4b8220b903..486b00dc3d6c1ced11ce3a900ea84ac5039e0d93 100644
--- a/blimp/client/core/render_widget/blimp_document_manager.h
+++ b/blimp/client/core/render_widget/blimp_document_manager.h
@@ -41,10 +41,9 @@ class BlimpDocumentManager
 
   bool OnTouchEvent(const ui::MotionEvent& motion_event);
 
-  // Notifies |callback| when all pending commits on the active BlimpCompositor
-  // have been drawn to the screen.  If the active compositor is destroyed or
-  // becomes hidden |callback| will be notified.
-  void NotifyWhenDonePendingCommits(base::Closure callback);
+  void RequestCopyOfCompositorOutput(
+      std::unique_ptr<cc::CopyOutputRequest> copy_request,
+      bool flush_pending_update);
 
   // Sends input event to the engine, virtual for testing.
   virtual void SendWebGestureEvent(int document_id,