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

cc/trees/layer_tree.h

Index: cc/trees/layer_tree.h
diff --git a/cc/trees/layer_tree.h b/cc/trees/layer_tree.h
new file mode 100644
index 0000000000000000000000000000000000000000..833fcc4afcd45c512f7d5fef771cd574ed3fa807
--- /dev/null
+++ b/cc/trees/layer_tree.h
@@ -0,0 +1,65 @@
+// Copyright 2016 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_H_
+#define CC_TREES_LAYER_TREE_H_
+
+#include <unordered_map>
+#include <unordered_set>
+
+#include "base/macros.h"
+#include "cc/base/cc_export.h"
+
+namespace cc {
+
+namespace proto {
+class LayerTree;
+class LayerUpdate;
+}
+
+class AnimationHost;
+class Layer;
+
+using LayerSet = std::unordered_set<Layer*>;
+using LayerIdMap = std::unordered_map<int, Layer*>;
+
+class CC_EXPORT LayerTree {
+ public:
+  explicit LayerTree(std::unique_ptr<AnimationHost>* animation_host);
+  ~LayerTree();
+
+  void RegisterLayer(Layer* layer);
+  void UnregisterLayer(Layer* layer);
+  Layer* LayerById(int id) const;
+
+  void AddLayerShouldPushProperties(Layer* layer);
+  void RemoveLayerShouldPushProperties(Layer* layer);
+  std::unordered_set<Layer*>& LayersThatShouldPushProperties();
+
+  void ToProtobuf(proto::LayerTree* proto);
+  void FromProtobuf(const proto::LayerTree& proto);
+
+  AnimationHost* animation_host() const { return animation_host_.get(); }
+
+  bool in_paint_layer_contents() const { return in_paint_layer_contents_; }
+  bool& get_in_paint_layer_contents() { return in_paint_layer_contents_; }
+  void set_in_paint_layer_contents(bool value);
+
+ private:
+  // Set of layers that need to push properties.
+  LayerSet layers_that_should_push_properties_;
+
+  // Layer id to Layer map.
+  LayerIdMap layer_id_map_;
+
+  bool in_paint_layer_contents_;
+
+  std::unique_ptr<AnimationHost> animation_host_;
+
+  DISALLOW_COPY_AND_ASSIGN(LayerTree);
+};
+
+}  // namespace cc
+
+#endif  // CC_TREES_LAYER_TREE_H_