mustash: enable GPU Compositing in renderer

content/renderer/render_widget_mus_connection.h

Index: content/renderer/render_widget_mus_connection.h
diff --git a/content/renderer/render_widget_mus_connection.h b/content/renderer/render_widget_mus_connection.h
index d82d67e628c0296fa2dd5f667c942025533282ea..e2be99a253cc98c24cc935879b34ad54f75eb2ae 100644
--- a/content/renderer/render_widget_mus_connection.h
+++ b/content/renderer/render_widget_mus_connection.h
@@ -6,6 +6,7 @@
 #define CONTENT_RENDERER_RENDER_WIDGET_MUS_CONNECTION_H_
 
 #include "base/macros.h"
+#include "components/mus/public/cpp/output_surface.h"
 #include "components/mus/public/cpp/window.h"
 #include "components/mus/public/cpp/window_observer.h"
 #include "components/mus/public/cpp/window_surface.h"
@@ -13,6 +14,10 @@
 #include "components/mus/public/cpp/window_tree_delegate.h"
 #include "mojo/public/cpp/bindings/binding.h"
 
+namespace {
+class OutputSurface;
+}  // namespace
+
 namespace content {
 
 class RenderWidgetMusConnection : public mus::WindowTreeDelegate,
@@ -23,6 +28,10 @@ class RenderWidgetMusConnection : public mus::WindowTreeDelegate,
       mojo::InterfaceRequest<mus::mojom::WindowTreeClient> request);
   ~RenderWidgetMusConnection() override;
 
+  scoped_ptr<cc::OutputSurface> CreateOutputSurface();
+
+  static RenderWidgetMusConnection* Get(int routing_id);
+
  private:
   void SubmitCompositorFrame();