cc/blimp: Add synchronization for scroll/scale state.

cc/blimp/remote_compositor_bridge_client.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_BLIMP_REMOTE_COMPOSITOR_BRIDGE_CLIENT_H_
 #define CC_BLIMP_REMOTE_COMPOSITOR_BRIDGE_CLIENT_H_
 
 #include <unordered_map>
 
 #include "base/macros.h"
 #include "cc/base/cc_export.h"
 
 namespace base {
 class SingleThreadTaskRunner;
 }  // namespace base
 
 namespace gfx {
 class ScrollOffset;
 }  // namespace gfx
 
 namespace cc {
+namespace proto {
+class ClientStateUpdate;
+}  // namespace proto
 class CompositorProtoState;
 
 class CC_EXPORT RemoteCompositorBridgeClient {
  public:
   using ScrollOffsetMap = std::unordered_map<int, gfx::ScrollOffset>;
 
   virtual ~RemoteCompositorBridgeClient() {}
 
   // Called in response to a ScheduleMainFrame request made on the
   // RemoteCompositorBridge.
   // Note: The method should always be invoked asynchronously after the request
   // is made.
   virtual void BeginMainFrame() = 0;
 
-  // Provides an update from the mutations made on the client. Returns true if
-  // the update could be successfully applied to the engine state. This can
-  // fail, for instance, if the layer present in the update was destroyed on the
-  // engine.
-  virtual bool ApplyScrollAndScaleUpdateFromClient(
-      const ScrollOffsetMap& client_scroll_map,
-      float client_page_scale) = 0;
+  // Applied state updates reported from the client onto the main thread state
+  // on the engine.
+  virtual void ApplyStateUpdateFromClient(
+      const proto::ClientStateUpdate& client_state_update) = 0;
 };
 
 }  // namespace cc
 
 #endif  // CC_BLIMP_REMOTE_COMPOSITOR_BRIDGE_CLIENT_H_