Teach the native viewport service to draw a Surface into itself

mojo/examples/compositor_app/compositor_app.cc

Index: mojo/examples/compositor_app/compositor_app.cc
diff --git a/mojo/examples/compositor_app/compositor_app.cc b/mojo/examples/compositor_app/compositor_app.cc
index 16a9184cf2fed20cc6559459717a1a299f847752..bbb7a07f10d41cac298216f0cd79a2155483ee86 100644
--- a/mojo/examples/compositor_app/compositor_app.cc
+++ b/mojo/examples/compositor_app/compositor_app.cc
@@ -37,6 +37,7 @@ class SampleApp : public ApplicationDelegate, public NativeViewportClient {
 
   virtual void OnCreated(uint64_t native_viewport_id) OVERRIDE {
     CommandBufferPtr cb;
+    // TODO(jamesr): Output to a surface instead.
     gpu_service_->CreateOnscreenGLES2Context(
         native_viewport_id, Size::From(gfx::Size(800, 600)), Get(&cb));
     host_.reset(new CompositorHost(cb.PassMessagePipe()));