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

cc/trees/layer_tree_host_common.h

 // Copyright 2011 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_TREES_LAYER_TREE_HOST_COMMON_H_
 #define CC_TREES_LAYER_TREE_HOST_COMMON_H_
 
 #include <stddef.h>
 
 #include <limits>
@@ skipping 155 matching lines @@
     ScrollbarsUpdateInfo();
     ScrollbarsUpdateInfo(int layer_id, bool hidden);
 
     bool operator==(const ScrollbarsUpdateInfo& other) const;
 
     void ToProtobuf(proto::ScrollbarsUpdateInfo* proto) const;
     void FromProtobuf(const proto::ScrollbarsUpdateInfo& proto);
   };
 };
 
+// A container for the state that was reported to the main thread during
+// BeginMainFrame, but could not be applied/resolved on the main thread.
+struct CC_EXPORT ReflectedMainFrameState {
+  struct ScrollUpdate {
+    int layer_id = Layer::LayerIdLabels::INVALID_ID;
+    gfx::Vector2dF scroll_delta;
+  };
+
+  ReflectedMainFrameState();
+  ~ReflectedMainFrameState();
+
+  std::vector<ScrollUpdate> scrolls;
+  float page_scale_delta;
+};
+
 struct CC_EXPORT ScrollAndScaleSet {
   ScrollAndScaleSet();
   ~ScrollAndScaleSet();
 
   // The inner viewport scroll delta is kept separate since it's special.
   // Because the inner (visual) viewport's maximum offset depends on the
   // current page scale, the two must be committed at the same time to prevent
   // clamping.
   LayerTreeHostCommon::ScrollUpdateInfo inner_viewport_scroll;
 
@@ skipping 32 matching lines @@
     function(tree_impl->LayerById(id));
   }
 }
 
 CC_EXPORT PropertyTrees* GetPropertyTrees(Layer* layer);
 CC_EXPORT PropertyTrees* GetPropertyTrees(LayerImpl* layer);
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_COMMON_H_