Add compile flag for enabling the compostior

sky/viewer/platform/weblayertreeview_impl.h

Index: sky/viewer/platform/weblayertreeview_impl.h
diff --git a/sky/viewer/platform/weblayertreeview_impl.h b/sky/viewer/platform/weblayertreeview_impl.h
index 7a072034ef3c0dff0495224144983855683dbbbf..ec6af96b6bab3fcb4a2843c9a4624f69274c6534 100644
--- a/sky/viewer/platform/weblayertreeview_impl.h
+++ b/sky/viewer/platform/weblayertreeview_impl.h
@@ -9,6 +9,8 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/single_thread_task_runner.h"
+#include "cc/layers/content_layer.h"
+#include "cc/layers/content_layer_client.h"
 #include "cc/trees/layer_tree_host_client.h"
 #include "mojo/cc/output_surface_mojo.h"
 #include "mojo/services/public/interfaces/gpu/gpu.mojom.h"
@@ -35,6 +37,7 @@ namespace sky {
 
 class WebLayerTreeViewImpl : public blink::WebLayerTreeView,
                              public cc::LayerTreeHostClient,
+                             public cc::ContentLayerClient,
                              public mojo::OutputSurfaceMojoClient {
  public:
   WebLayerTreeViewImpl(
@@ -43,7 +46,7 @@ class WebLayerTreeViewImpl : public blink::WebLayerTreeView,
       mojo::GpuPtr gpu_service);
   virtual ~WebLayerTreeViewImpl();
 
-  void set_widget(blink::WebWidget* widget) { widget_ = widget; }
+  void set_widget(blink::WebWidget* widget);
   void set_view(mojo::View* view) { view_ = view; }
 
   // cc::LayerTreeHostClient implementation.
@@ -66,6 +69,12 @@ class WebLayerTreeViewImpl : public blink::WebLayerTreeView,
   virtual void DidCompleteSwapBuffers() override;
   virtual void RateLimitSharedMainThreadContext() override {}
 
+  // cc::ContentLayerClient
+  void PaintContents(SkCanvas* canvas,
+                     const gfx::Rect& clip,
+                     GraphicsContextStatus gc_status) override;
+  bool FillsBoundsCompletely() const override;
+
   // blink::WebLayerTreeView implementation.
   virtual void setSurfaceReady() override;
   virtual void setRootLayer(const blink::WebLayer& layer) override;
@@ -122,6 +131,8 @@ class WebLayerTreeViewImpl : public blink::WebLayerTreeView,
       main_thread_compositor_task_runner_;
   base::WeakPtr<WebLayerTreeViewImpl> main_thread_bound_weak_ptr_;
 
+  scoped_refptr<cc::ContentLayer> root_layer_;
+
   base::WeakPtrFactory<WebLayerTreeViewImpl> weak_factory_;
   DISALLOW_COPY_AND_ASSIGN(WebLayerTreeViewImpl);
 };