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

mojo/services/gpu/public/interfaces/gpu.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/viewport_parameter_listener.mojom";
 
 interface Gpu {
-  CreateOnscreenGLES2Context(uint64 native_viewport_id,
-                             Size size,
-                             CommandBuffer& gles2_client,
-                             ViewportParameterListener? listener);
+  // Creates a new offscreen OpenGL ES 2.0 context.
   CreateOffscreenGLES2Context(CommandBuffer& gles2_client);
 };
+
+// A ContextProvider can be used to provide new command buffers related to a
+// particular context, for instance configured to draw to a particular display.
+interface ContextProvider {
+  // This initializes a new command buffer for this provider when available,
+  // closing connections to the previously created command buffer (if any).
+  //
+  // This call may not return for an extended period of time if a command
+  // buffer cannot be produced immediately, for example if it is associated
+  // with a view that is offscreen.
+  //
+  // If a viewport_parameter_listener is provided it will be when vsync

[qsr, 2015/02/20 11:25:47]

It seems you are missing some part of this sentence.

[jamesr, 2015/02/20 22:01:05]

Done.

+  // parameters change for this context.
+  Create(ViewportParameterListener? viewport_parameter_listener)
+      => (CommandBuffer? gles2_client);
+};