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..0850afe681554f32aa445ce68931667d6e270327
--- /dev/null
+++ b/cc/trees/layer_tree.h
@@ -0,0 +1,46 @@
+// 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 Layer;
+
+using LayerSet = std::unordered_set<Layer*>;
+using LayerIdMap = std::unordered_map<int, Layer*>;
+
+class CC_EXPORT LayerTree {

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

I would suggest move Register/UnregisterLayer to the LayerTree as well. And the
methods that return the LayerListIterator. And have the dependent call sites use
the LayerTree instead.

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

Register/UnregisterLayer moved to LayerTree.

+ public:
+  LayerTree();
+  ~LayerTree();
+
+  void AddLayerShouldPushProperties(Layer* layer);
+  void RemoveLayerShouldPushProperties(Layer* layer);
+
+  void ToProtobuf(proto::LayerTree* proto);
+  void FromProtobuf(const proto::LayerTree& proto, LayerIdMap* layer_id_map);

[Khushal, 2016/07/18 16:59:32]

The LayerIdMap would move to the LayerTree, wouldn't need to pass it in here
then.

[xingliu, 2016/07/19 22:47:37]

Done.

+  LayerSet& layers_that_should_push_properties();

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

You shouldn't have to expose this after you move the methods above.

[xingliu, 2016/07/19 22:47:37]

Done.

+
+ private:
+  // Set of layers that need to push properties.
+  LayerSet layers_that_should_push_properties_;
+
+  DISALLOW_COPY_AND_ASSIGN(LayerTree);
+};
+
+}  // namespace cc
+
+#endif  // CC_TREES_LAYER_TREE_H_