Add a Display and ContextProvider concept to mojom, use to recreate

mojo/services/native_viewport/public/interfaces/native_viewport.mojom

 // Copyright 2014 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.
 
 module mojo;
 
 import "geometry/public/interfaces/geometry.mojom";
-import "gpu/public/interfaces/command_buffer.mojom";
+import "gpu/public/interfaces/context_provider.mojom";
 import "input_events/public/interfaces/input_events.mojom";
-import "surfaces/public/interfaces/surface_id.mojom";
 
 struct ViewportMetrics {
   Size size;
   float device_pixel_ratio = 1.0;
 };
 
 interface NativeViewport {
   // TODO(sky): having a create function is awkward. Should there be a factory
   // to create the NativeViewport that takes the size?
-  Create(Size size) => (uint64 native_viewport_id, ViewportMetrics metrics);
+  Create(Size size) => (ViewportMetrics metrics);
 
   Show();
   Hide();
   Close();
   SetSize(Size size);
-  SubmittedFrame(SurfaceId surface_id);
   SetEventDispatcher(NativeViewportEventDispatcher dispatcher);
 
+  // Requests a ContextProvider capable of producing contexts that draw to
+  // this native viewport.
+  GetContextProvider(ContextProvider& provider);
+
   // The initial viewport metrics will be sent in the reply to the Create
   // method. Call RequestMetrics() to receive updates when the viewport metrics
   // change. The reply will be sent when the viewport metrics are different from
   // the values last sent, so to receive continuous updates call this method
   // again after receiving the callback.
   RequestMetrics() => (ViewportMetrics metrics);
 };
 
 interface NativeViewportEventDispatcher {
   OnEvent(Event event) => ();
 };