Re-land: cc: Use worker context for one-copy tile initialization.

cc/output/context_provider.h

 // Copyright (c) 2013 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.
 
 #ifndef CC_OUTPUT_CONTEXT_PROVIDER_H_
 #define CC_OUTPUT_CONTEXT_PROVIDER_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
+#include "base/synchronization/lock.h"
 #include "cc/base/cc_export.h"
 #include "gpu/command_buffer/common/capabilities.h"
 
 class GrContext;
 
 namespace base {
 class Lock;
 }
 
 namespace gpu {
 class ContextSupport;
 namespace gles2 { class GLES2Interface; }
 }
 
 namespace cc {
 struct ManagedMemoryPolicy;
 
 class ContextProvider : public base::RefCountedThreadSafe<ContextProvider> {
  public:
+  class ScopedContextGL {

[piman, 2015/07/23 20:44:52]

nit: I like this class but kinda hate the name. Maybe add a Lock somewhere?

[reveman, 2015/07/24 17:49:15]

Changed the name to ScopedContextLock.

+   public:
+    explicit ScopedContextGL(ContextProvider* context_provider)
+        : context_provider_(context_provider),
+          context_lock_(*context_provider_->GetLock()) {
+      // Allow current thread to bind to |context_provider|.
+      context_provider_->DetachFromThread();
+    }
+    ~ScopedContextGL() {
+      // Allow a different thread to bind to |context_provider|.
+      context_provider_->DetachFromThread();
+    }
+
+    gpu::gles2::GLES2Interface* ContextGL() {
+      return context_provider_->ContextGL();
+    }
+
+   private:
+    ContextProvider* const context_provider_;
+    base::AutoLock context_lock_;
+  };
   // Bind the 3d context to the current thread. This should be called before
   // accessing the contexts. Calling it more than once should have no effect.
   // Once this function has been called, the class should only be accessed
   // from the same thread.
   virtual bool BindToCurrentThread() = 0;
   virtual void DetachFromThread() {}
 
   virtual gpu::gles2::GLES2Interface* ContextGL() = 0;
   virtual gpu::ContextSupport* ContextSupport() = 0;
   virtual class GrContext* GrContext() = 0;
@@ skipping 47 matching lines @@
       const MemoryPolicyChangedCallback& memory_policy_changed_callback) = 0;
 
  protected:
   friend class base::RefCountedThreadSafe<ContextProvider>;
   virtual ~ContextProvider() {}
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_CONTEXT_PROVIDER_H_