Revert "gpu: Use mojom API for creating gpu channel."

services/ui/gpu/interfaces/gpu_service.mojom

 // Copyright 2016 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 ui.mojom;
 
 import "cc/ipc/display_compositor.mojom";
 import "gpu/ipc/common/gpu_info.mojom";
 import "gpu/ipc/common/memory_stats.mojom";
 import "gpu/ipc/common/surface_handle.mojom";
 import "gpu/ipc/common/sync_token.mojom";
 import "ui/gfx/geometry/mojo/geometry.mojom";
 import "ui/gfx/mojo/buffer_types.mojom";
 
 interface GpuService {
   // Tells the GPU service to create a new channel for communication with a
   // client. The GPU service responds with an IPC handle.
   EstablishGpuChannel(int32 client_id,
                       uint64 client_tracing_id,
                       bool is_gpu_host)
-      => (handle<message_pipe>? channel_handle);
+      => (handle<message_pipe> channel_handle);
 
   [Sync]
   CreateGpuMemoryBuffer(gfx.mojom.GpuMemoryBufferId id,
                         gfx.mojom.Size size,
                         gfx.mojom.BufferFormat format,
                         gfx.mojom.BufferUsage usage,
                         int32 client_id,
                         gpu.mojom.SurfaceHandle surface_handle)
       => (gfx.mojom.GpuMemoryBufferHandle buffer_handle);
 
   DestroyGpuMemoryBuffer(gfx.mojom.GpuMemoryBufferId id,
                          int32 client_id,
                          gpu.mojom.SyncToken sync_token);
 
   GetVideoMemoryUsageStats() => (gpu.mojom.VideoMemoryUsageStats stats);
 };