Add the ability to create child scenes

This patch contains Dart bindings for adding a child scene when running in
Mozart. The child scene is currently ignored, but a later patch will actually
incoporate it into the tree.

engine/src/flutter/flow/BUILD.gn

@@ -16,6 +16,8 @@ source_set("flow") {
     "color_filter_layer.h",
     "container_layer.cc",
     "container_layer.h",
+    "child_scene_layer.cc",
+    "child_scene_layer.h",
     "instrumentation.cc",
     "instrumentation.h",
     "layer.cc",
@@ -41,5 +43,6 @@ source_set("flow") {
   deps = [
     "//base",
     "//skia",
+    "//mojo/services/gfx/composition/interfaces",
   ]
 }

engine/src/flutter/flow/child_scene_layer.cc

@@ -0,0 +1,18 @@
+// 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.
+
+#include "flow/child_scene_layer.h"
+
+namespace flow {
+
+ChildSceneLayer::ChildSceneLayer() {
+}
+
+ChildSceneLayer::~ChildSceneLayer() {
+}
+
+void ChildSceneLayer::Paint(PaintContext::ScopedFrame& frame) {
+}
+
+}  // namespace flow

engine/src/flutter/flow/child_scene_layer.h

@@ -0,0 +1,40 @@
+// 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 FLOW_CHILD_SCENE_LAYER_H_
+#define FLOW_CHILD_SCENE_LAYER_H_
+
+#include "flow/layer.h"
+#include "mojo/services/gfx/composition/interfaces/scenes.mojom.h"
+
+namespace flow {
+
+class ChildSceneLayer : public Layer {
+ public:
+  ChildSceneLayer();
+  ~ChildSceneLayer() override;
+
+  void set_offset(const SkPoint& offset) { offset_ = offset; }
+
+  void set_physical_size(const SkISize& physical_size) {
+    physical_size_ = physical_size;
+  }
+
+  void set_scene_token(mojo::gfx::composition::SceneTokenPtr scene_token) {
+    scene_token_ = scene_token.Pass();
+  }
+
+  void Paint(PaintContext::ScopedFrame& frame) override;
+
+ private:
+  SkPoint offset_;
+  SkISize physical_size_;
+  mojo::gfx::composition::SceneTokenPtr scene_token_;
+
+  DISALLOW_COPY_AND_ASSIGN(ChildSceneLayer);
+};
+
+}  // namespace flow
+
+#endif  // FLOW_CHILD_SCENE_LAYER_H_