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

third_party/WebKit/Source/platform/graphics/gpu/DrawingBufferTest.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 225 matching lines @@
 class WebGraphicsContext3DProviderForTests : public WebGraphicsContext3DProvider {
 public:
     WebGraphicsContext3DProviderForTests(PassOwnPtr<gpu::gles2::GLES2Interface> gl)
         : m_gl(std::move(gl))
     {
     }
 
     gpu::gles2::GLES2Interface* contextGL() override { return m_gl.get(); }
     // Not used by WebGL code.
     GrContext* grContext() override { return nullptr; }
+    void DetachFromThread() override {}
     gpu::Capabilities getCapabilities()
     {
         return gpu::Capabilities();
     }
     void setLostContextCallback(WebClosure) {}
     void setErrorMessageCallback(WebFunction<void(const char*, int32_t id)>) {}
 
 private:
     OwnPtr<gpu::gles2::GLES2Interface> m_gl;
 };
@@ skipping 504 matching lines @@
     m_drawingBuffer->markContentsChanged();
     EXPECT_TRUE(m_drawingBuffer->prepareMailbox(&mailbox, 0));
     EXPECT_EQ(initialSize, m_gl->mostRecentlyProducedSize());
     EXPECT_FALSE(mailbox.allowOverlay);
 
     m_drawingBuffer->mailboxReleased(mailbox, false);
     m_drawingBuffer->beginDestruction();
 }
 
 } // namespace blink