Transfer LayerImpl ownership to LayerTreeImpl

cc/layers/layer_collections.h

Index: cc/layers/layer_collections.h
diff --git a/cc/layers/layer_collections.h b/cc/layers/layer_collections.h
new file mode 100644
index 0000000000000000000000000000000000000000..6830261629e6713dd531a3979831727bec134689
--- /dev/null
+++ b/cc/layers/layer_collections.h
@@ -0,0 +1,27 @@
+// 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_LAYERS_LAYER_COLLECTIONS_H_
+#define CC_LAYERS_LAYER_COLLECTIONS_H_
+
+#include <unordered_map>
+#include <vector>
+
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "cc/base/cc_export.h"
+
+namespace cc {
+class Layer;
+class LayerImpl;
+
+using LayerList = std::vector<scoped_refptr<Layer>>;
+using OwnedLayerImplList = std::vector<scoped_ptr<LayerImpl>>;
+using LayerImplList = std::vector<LayerImpl*>;
+using OwnedLayerImplMap = std::unordered_map<int, scoped_ptr<LayerImpl>>;
+using LayerImplMap = std::unordered_map<int, LayerImpl*>;
+
+}  // namespace cc
+
+#endif  // CC_LAYERS_LAYER_COLLECTIONS_H_