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

ui/ozone/gpu/gpu_memory_buffer_factory_ozone_native_buffer.h

Index: ui/ozone/gpu/gpu_memory_buffer_factory_ozone_native_buffer.h
diff --git a/ui/ozone/gpu/gpu_memory_buffer_factory_ozone_native_buffer.h b/ui/ozone/gpu/gpu_memory_buffer_factory_ozone_native_buffer.h
index 006a4a5497ac72a7242ce4506e0ceee8de39bd3b..f449bbb82af61a48d569bf86ed9454278709d861 100644
--- a/ui/ozone/gpu/gpu_memory_buffer_factory_ozone_native_buffer.h
+++ b/ui/ozone/gpu/gpu_memory_buffer_factory_ozone_native_buffer.h
@@ -9,6 +9,7 @@
 
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/lock.h"
+#include "base/threading/thread_checker.h"
 #include "ui/gfx/geometry/size.h"
 #include "ui/gfx/gpu_memory_buffer.h"
 #include "ui/gfx/native_widget_types.h"
@@ -31,6 +32,7 @@ class OZONE_GPU_EXPORT GpuMemoryBufferFactoryOzoneNativeBuffer {
   virtual ~GpuMemoryBufferFactoryOzoneNativeBuffer();
 
   // Creates a GPU memory buffer identified by |id|.
+  // It can be called on any thread.
   bool CreateGpuMemoryBuffer(gfx::GpuMemoryBufferId id,
                              const gfx::Size& size,
                              gfx::GpuMemoryBuffer::Format format,
@@ -39,6 +41,7 @@ class OZONE_GPU_EXPORT GpuMemoryBufferFactoryOzoneNativeBuffer {
                              gfx::PluginWindowHandle surface_handle);
 
   // Destroys GPU memory buffer identified by |id|.
+  // It can be called on any thread.
   void DestroyGpuMemoryBuffer(gfx::GpuMemoryBufferId id, int client_id);
 
   // Creates a GLImage instance for GPU memory buffer identified by |id|.
@@ -58,6 +61,7 @@ class OZONE_GPU_EXPORT GpuMemoryBufferFactoryOzoneNativeBuffer {
  private:
   BufferToPixmapMap native_pixmap_map_;
   base::Lock native_pixmap_map_lock_;
+  base::ThreadChecker thread_checker_;
 };
 
 }  // namespace ui