WIP - compositor worker mega patch.

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 6d4ba2677e79b7176f54134d07133d35ef72d012..08208d31da6d4e53219242c2fc9f20a906cac440 100644
--- a/cc/trees/layer_tree_impl.h
+++ b/cc/trees/layer_tree_impl.h
@@ -37,6 +37,7 @@ namespace cc {
 class ContextProvider;
 class DebugRectHistory;
 class FrameRateCounter;
+class ElementLayers;
 class HeadsUpDisplayLayerImpl;
 class LayerExternalScrollOffsetListener;
 class LayerScrollOffsetDelegate;
@@ -115,6 +116,7 @@ class CC_EXPORT LayerTreeImpl {
   bool RequiresHighResToDraw() const;
   bool SmoothnessTakesPriority() const;
   VideoFrameControllerClient* GetVideoFrameControllerClient() const;
+  LayerTreeHostImpl* host() const { return layer_tree_host_impl_; }
 
   // Tree specific methods exposed to layer-impl tree.
   // ---------------------------------------------------------------------------
@@ -142,6 +144,19 @@ class CC_EXPORT LayerTreeImpl {
 
   void PushPropertiesTo(LayerTreeImpl* tree_impl);
 
+  // TODO(sad): This is ... not really nice. Should be cleaner maybe.
+  // vollick: What's wrong with it? Just the names or the fact that we have a
+  // proxy registry on the layer tree host impl?
+  void AddToElementMap(LayerImpl* layer);
+  void RemoveFromElementMap(LayerImpl* layer);
+
+  struct ElementLayers {
+    LayerImpl* main = nullptr;
+    LayerImpl* scroll = nullptr;
+  };
+
+  bool GetMutableLayers(uint64_t element_id, ElementLayers* element_layers);
+
   int source_frame_number() const { return source_frame_number_; }
   void set_source_frame_number(int frame_number) {
     source_frame_number_ = frame_number;
@@ -477,6 +492,8 @@ class CC_EXPORT LayerTreeImpl {
   typedef base::hash_map<int, LayerImpl*> LayerIdMap;
   LayerIdMap layer_id_map_;
 
+  std::map<uint64_t, ElementLayers> element_layers_map_;
+
   // 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.)