layers: Consolidate the ownership of layers in views::View and aura::Window.

ui/compositor/layer_owner.cc

+// Copyright (c) 2012 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.
+
+#include "ui/compositor/layer_owner.h"
+
+namespace ui {
+
+LayerOwner::LayerOwner()
+    : layer_(NULL) {
+}
+
+LayerOwner::~LayerOwner() {
+}
+
+Layer* LayerOwner::AcquireLayer() {
+  return layer_owner_.release();
+}
+
+}  // namespace ui