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

content/renderer/webgraphicscontext3d_provider_impl.cc

Index: content/renderer/webgraphicscontext3d_provider_impl.cc
diff --git a/content/renderer/webgraphicscontext3d_provider_impl.cc b/content/renderer/webgraphicscontext3d_provider_impl.cc
index 17f34bc3a8ffbca219da56ec8ecf0e72a2f89b3e..1dbb6e529fd197bea546ea1ee83e3bf090bb5cdb 100644
--- a/content/renderer/webgraphicscontext3d_provider_impl.cc
+++ b/content/renderer/webgraphicscontext3d_provider_impl.cc
@@ -6,6 +6,7 @@
 
 #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 {
@@ -20,6 +21,12 @@ 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();
 }