Implement offscreenCanvas.getContext('webgl') on a worker thread

content/renderer/webgraphicscontext3d_provider_impl.cc

 // 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.
 
 #include "content/renderer/webgraphicscontext3d_provider_impl.h"
 
 #include "content/common/gpu/client/context_provider_command_buffer.h"
 #include "gpu/command_buffer/client/context_support.h"
+#include "gpu/ipc/client/command_buffer_proxy_impl.h"
 #include "third_party/WebKit/public/platform/functional/WebFunction.h"
 
 namespace content {
 
 WebGraphicsContext3DProviderImpl::WebGraphicsContext3DProviderImpl(
     scoped_refptr<ContextProviderCommandBuffer> provider)
     : provider_(std::move(provider)) {}
 
 WebGraphicsContext3DProviderImpl::~WebGraphicsContext3DProviderImpl() {}
 
 gpu::gles2::GLES2Interface* WebGraphicsContext3DProviderImpl::contextGL() {
   return provider_->ContextGL();
 }
 
+void WebGraphicsContext3DProviderImpl::DetachFromThread() {

[Ken Russell (switch to Gerrit), 2016/05/04 21:02:56]

I'm very uncomfortable with using these primitives. Please refactor
RendererBlinkPlatformImpl::createOffscreenGraphicsContext3DProvider so that,
optionally, BindToCurrentThread isn't called in the first place. Then the worker
thread can be the first to call BindToCurrentThread on the newly-created
ContextProviderCommandBuffer.

+  provider_->GetCommandBufferProxy()->DetachFromThread();
+  provider_->DetachFromThread();
+  provider_->BindToCurrentThread();
+}
+
 GrContext* WebGraphicsContext3DProviderImpl::grContext() {
   return provider_->GrContext();
 }
 
 gpu::Capabilities WebGraphicsContext3DProviderImpl::getCapabilities() {
   return provider_->ContextCapabilities();
 }
 
 void WebGraphicsContext3DProviderImpl::setLostContextCallback(
     blink::WebClosure c) {
   provider_->SetLostContextCallback(c.TakeBaseCallback());
 }
 
 void WebGraphicsContext3DProviderImpl::setErrorMessageCallback(
     blink::WebFunction<void(const char*, int32_t)> c) {
   provider_->ContextSupport()->SetErrorMessageCallback(c.TakeBaseCallback());
 }
 
 }  // namespace content