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 91e346686d1367e8b497277d64772ca9ed4e4f1b..83123d221fa015eed2fac15fce8691d697bd88fc 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;
@@ -111,6 +112,7 @@ 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.
   // ---------------------------------------------------------------------------
@@ -485,6 +487,8 @@ class CC_EXPORT LayerTreeImpl {
   typedef base::hash_map<int, LayerImpl*> LayerIdMap;
   LayerIdMap layer_id_map_;
 
+  // TODO(vollick): this should be owned and maintained in blink (most likely by
+  // the compositor mutator client).
   base::hash_map<uint64_t, ElementLayers> element_layers_map_;
 
   // Maps from clip layer ids to scroll layer ids.  Note that this only includes