zero-copy: Clarify to allocate/destroy GpuMemoryBuffer on any thread and use it on the main thread o

content/common/gpu/gpu_memory_buffer_factory.h

 // 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.
 
 #ifndef CONTENT_COMMON_GPU_GPU_MEMORY_BUFFER_FACTORY_H_
 #define CONTENT_COMMON_GPU_GPU_MEMORY_BUFFER_FACTORY_H_
 
 #include <vector>
 
 #include "base/memory/ref_counted.h"
@@ skipping 13 matching lines @@
 
 namespace content {
 
 class CONTENT_EXPORT GpuMemoryBufferFactory {
  public:
   struct Configuration {
     gfx::GpuMemoryBuffer::Format format;
     gfx::GpuMemoryBuffer::Usage usage;
   };
 
-  GpuMemoryBufferFactory() {}
   virtual ~GpuMemoryBufferFactory() {}
 
   // Gets system supported GPU memory buffer factory types. Preferred type at
   // the front of vector.
   static void GetSupportedTypes(std::vector<gfx::GpuMemoryBufferType>* types);
 
   // Creates a new factory instance for |type|.
   static scoped_ptr<GpuMemoryBufferFactory> Create(
       gfx::GpuMemoryBufferType type);
 
   // Gets supported format/usage configurations.
   virtual void GetSupportedGpuMemoryBufferConfigurations(
       std::vector<Configuration>* configurations) = 0;
 
   // Creates a new GPU memory buffer instance. A valid handle is returned on
-  // success.
+  // success. It can be called on any thread.
   virtual gfx::GpuMemoryBufferHandle CreateGpuMemoryBuffer(
       gfx::GpuMemoryBufferId id,
       const gfx::Size& size,
       gfx::GpuMemoryBuffer::Format format,
       gfx::GpuMemoryBuffer::Usage usage,
       int client_id,
       gfx::PluginWindowHandle surface_handle) = 0;
 
   // Destroys GPU memory buffer identified by |id|.
+  // It can be called on any thread.
   virtual void DestroyGpuMemoryBuffer(gfx::GpuMemoryBufferId id,
                                       int client_id) = 0;
 
   // Type-checking downcast routine.
   virtual gpu::ImageFactory* AsImageFactory() = 0;
 
+ protected:
+  GpuMemoryBufferFactory() {}
+
  private:
   DISALLOW_COPY_AND_ASSIGN(GpuMemoryBufferFactory);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_GPU_GPU_MEMORY_BUFFER_FACTORY_H_