compositor-worker: Introduce WebCompositorMutableState

cc/trees/layer_tree_impl.h

Index: cc/trees/layer_tree_impl.h
diff --git a/cc/trees/layer_tree_impl.h b/cc/trees/layer_tree_impl.h
index 60ef91e2302df204c9b463faa7e36d1f10db0f52..b1761e6f7950d0d0418faf48a2cf27ce9065afd7 100644
--- a/cc/trees/layer_tree_impl.h
+++ b/cc/trees/layer_tree_impl.h
@@ -34,6 +34,7 @@ namespace cc {
 class ContextProvider;
 class DebugRectHistory;
 class FrameRateCounter;
+class ElementLayers;
 class HeadsUpDisplayLayerImpl;
 class LayerExternalScrollOffsetListener;
 class LayerScrollOffsetDelegate;
@@ -136,6 +137,11 @@ class CC_EXPORT LayerTreeImpl {
 
   void PushPropertiesTo(LayerTreeImpl* tree_impl);
 
+  void AddToElementMap(LayerImpl* layer);
+  void RemoveFromElementMap(LayerImpl* layer);
+  bool GetMutableLayers(uint64_t element_id,
+                        LayerImpl** main_layer,
+                        LayerImpl** scroll_layer);
   int source_frame_number() const { return source_frame_number_; }
   void set_source_frame_number(int frame_number) {
     source_frame_number_ = frame_number;
@@ -451,6 +457,8 @@ class CC_EXPORT LayerTreeImpl {
   typedef base::hash_map<int, LayerImpl*> LayerIdMap;
   LayerIdMap layer_id_map_;
 
+  std::map<uint64_t, ElementLayers> element_layers_map_;

[esprehn, 2015/11/16 20:01:04]

does the order matter here? Why map instead of hash map?

[Ian Vollick, 2015/11/18 17:20:33]

Done.

+
   // Maps from clip layer ids to scroll layer ids.  Note that this only includes
   // the subset of clip layers that act as scrolling containers.  (This is
   // derived from LayerImpl::scroll_clip_layer_ and exists to avoid O(n) walks.)