gpu: Have GpuService create and own GpuMemoryBufferFactory.

gpu/ipc/service/gpu_memory_buffer_factory.h

Index: gpu/ipc/service/gpu_memory_buffer_factory.h
diff --git a/gpu/ipc/service/gpu_memory_buffer_factory.h b/gpu/ipc/service/gpu_memory_buffer_factory.h
index 539caa8b3a6c191acf3fb52d47312eebb5c49707..55c83dc14b7dface59341fb686c6cdc608c984d1 100644
--- a/gpu/ipc/service/gpu_memory_buffer_factory.h
+++ b/gpu/ipc/service/gpu_memory_buffer_factory.h
@@ -23,7 +23,8 @@ class GPU_EXPORT GpuMemoryBufferFactory {
  public:
   virtual ~GpuMemoryBufferFactory() {}
 
-  // Creates a new factory instance for native GPU memory buffers.
+  // Creates a new factory instance for native GPU memory buffers. Returns null
+  // if native buffers are not supported.
   static std::unique_ptr<GpuMemoryBufferFactory> CreateNativeType();
 
   // Creates a new GPU memory buffer instance. A valid handle is returned on