Implement MusContextFactory::SharedMainThreadContextProvider()

ui/aura/mus/mus_context_factory.cc

Index: ui/aura/mus/mus_context_factory.cc
diff --git a/ui/aura/mus/mus_context_factory.cc b/ui/aura/mus/mus_context_factory.cc
index 71698063c0639e72494947b2103a2a4bd99dbcfc..e0ea1a0170b55edbecc0e52d9c071d53a850439b 100644
--- a/ui/aura/mus/mus_context_factory.cc
+++ b/ui/aura/mus/mus_context_factory.cc
@@ -62,8 +62,18 @@ void MusContextFactory::CreateCompositorFrameSink(
 
 scoped_refptr<cc::ContextProvider>
 MusContextFactory::SharedMainThreadContextProvider() {
-  // NOTIMPLEMENTED();
-  return nullptr;
+  if (!shared_main_thread_context_provider_) {
+    // In this point, the gpu channel should be already established in gpu_,
+    // the gpu_->EstablishGpuChannelSync() just returns the gpu channel
+    // immediately.

[sadrul, 2017/05/16 19:34:27]

Can you verify that here? i.e. have a bool flag that gets turned on in
::OnEstablishedGpuChannel() above, and either DCHECK() on the flag here, or
return nullptr if the flag is not set.

[Peng, 2017/05/16 19:52:08]

I think we shouldn't DCHECK it, because ui::ContextFactory is defined in this
way. In most case, the GpuChannel has been established, if not we have to
establish the channel synchronously. Also see [1], we also do the sync IPC in
GpuProcessTransportFactory::SharedMainThreadContextProvider().

[1]
https://cs.chromium.org/chromium/src/content/browser/compositor/gpu_process_t...

[sadrul, 2017/05/16 19:53:27]

If we cannot depend on this, can you remove/update the comment?

[Peng, 2017/05/16 19:56:55]

Removed. Done

+    scoped_refptr<gpu::GpuChannelHost> gpu_channel =
+        gpu_->EstablishGpuChannelSync();
+    shared_main_thread_context_provider_ =
+        gpu_->CreateContextProvider(std::move(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) {