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

cc/proto/client_state_update.proto

 // 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.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
+import "vector2d.proto";
+
 package cc.proto;
 
-message CommitEarlyOutReason {
-  enum Reason {
-    ABORTED_COMPOSITOR_FRAME_SINK_LOST = 1;
-    ABORTED_NOT_VISIBLE = 2;
-    ABORTED_DEFERRED_COMMIT = 3;
-    FINISHED_NO_UPDATES = 4;
-  }
+message ScrollUpdate {
+  optional int32 layer_id = 1;
+  optional Vector2d scroll_delta = 2;
+}
 
-  optional Reason reason = 1;
-}
+message ClientStateUpdate {
+  repeated ScrollUpdate scroll_updates = 1;
+  optional float page_scale_delta = 2;
+}