Implement aura::WindowPortMus::CreateCompositorFrameSink()

ui/aura/mus/mus_context_factory.cc

 // Copyright 2015 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.
 
 #include "ui/aura/mus/mus_context_factory.h"
 
 #include "base/memory/ptr_util.h"
 #include "services/ui/public/cpp/gpu/gpu.h"
 #include "ui/aura/mus/window_port_mus.h"
 #include "ui/aura/window_tree_host.h"
@@ skipping 32 matching lines @@
 
 void MusContextFactory::CreateCompositorFrameSink(
     base::WeakPtr<ui::Compositor> compositor) {
   gpu_->EstablishGpuChannel(
       base::Bind(&MusContextFactory::OnEstablishedGpuChannel,
                  weak_ptr_factory_.GetWeakPtr(), compositor));
 }
 
 scoped_refptr<cc::ContextProvider>
 MusContextFactory::SharedMainThreadContextProvider() {
-  // NOTIMPLEMENTED();
-  return nullptr;
+  if (!shared_main_thread_context_provider_) {
+    scoped_refptr<gpu::GpuChannelHost> gpu_channel =
+        gpu_->EstablishGpuChannelSync();
+    shared_main_thread_context_provider_ =
+        gpu_->CreateContextProvider(gpu_channel);
+    if (!shared_main_thread_context_provider_->BindToCurrentThread())
+      shared_main_thread_context_provider_ = nullptr;
+  }
+  return shared_main_thread_context_provider_;
 }
 
 void MusContextFactory::RemoveCompositor(ui::Compositor* compositor) {
   // NOTIMPLEMENTED();
 }
 
 double MusContextFactory::GetRefreshRate() const {
   return 60.0;
 }
 
 uint32_t MusContextFactory::GetImageTextureTarget(gfx::BufferFormat format,
                                                   gfx::BufferUsage usage) {
   // TODO(sad): http://crbug.com/675431
   return GL_TEXTURE_2D;
 }
 
 gpu::GpuMemoryBufferManager* MusContextFactory::GetGpuMemoryBufferManager() {
   return gpu_->gpu_memory_buffer_manager();
 }
 
 cc::TaskGraphRunner* MusContextFactory::GetTaskGraphRunner() {
   return raster_thread_helper_.task_graph_runner();
 }
 
 }  // namespace aura