Setup LayerTree class, refactor 2 functions from LayerTreeHost to it.

cc/trees/layer_tree_host.h

Index: cc/trees/layer_tree_host.h
diff --git a/cc/trees/layer_tree_host.h b/cc/trees/layer_tree_host.h
index 5628309c5456a558f5d3bfd0a65ae6bc504fae54..03ac81973fa79298bde746ee12c41a9271102d17 100644
--- a/cc/trees/layer_tree_host.h
+++ b/cc/trees/layer_tree_host.h
@@ -40,6 +40,7 @@
 #include "cc/resources/scoped_ui_resource.h"
 #include "cc/surfaces/surface_sequence.h"
 #include "cc/trees/compositor_mode.h"
+#include "cc/trees/layer_tree.h"
 #include "cc/trees/layer_tree_host_client.h"
 #include "cc/trees/layer_tree_settings.h"
 #include "cc/trees/mutator_host_client.h"
@@ -426,6 +427,8 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
     return client_picture_cache_ ? client_picture_cache_.get() : nullptr;
   }
 
+  LayerTree* layer_tree() { return &layer_tree_; }

[Khushal, 2016/07/18 16:59:33]

Can you change this to LayerTree* GetLayerTree() const; and define in the
header? When the method is added to the LayerTreeHost interface it won't be an
accessor.

[xingliu, 2016/07/19 22:47:38]

Done.

+
  protected:
   LayerTreeHost(InitParams* params, CompositorMode mode);
   void InitializeThreaded(
@@ -599,13 +602,13 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
   using ElementLayersMap = std::unordered_map<ElementId, Layer*, ElementIdHash>;
   ElementLayersMap element_layers_map_;
 
-  // Set of layers that need to push properties.
-  std::unordered_set<Layer*> layers_that_should_push_properties_;
-
   uint32_t surface_client_id_;
   uint32_t next_surface_sequence_;
   uint32_t num_consecutive_frames_suitable_for_gpu_ = 0;
 
+  // Layer tree that hold layers.
+  LayerTree layer_tree_;
+
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHost);
 };