Add support for EXT_image_flush_external extension

gpu/command_buffer/service/gl_stream_texture_image.h

Index: gpu/command_buffer/service/gl_stream_texture_image.h
diff --git a/gpu/command_buffer/service/gl_stream_texture_image.h b/gpu/command_buffer/service/gl_stream_texture_image.h
index b5bc370c5ba58af945a348050c9229c9f7fc5b40..0525a37adeceb22822b7a77ff60d165976bfd64c 100644
--- a/gpu/command_buffer/service/gl_stream_texture_image.h
+++ b/gpu/command_buffer/service/gl_stream_texture_image.h
@@ -31,6 +31,9 @@ class GPU_EXPORT GLStreamTextureImage : public gl::GLImage {
     matrix[13] += matrix[5];
     matrix[5] = -matrix[5];
   }
+
+  void Flush() override {}
+
  protected:
   ~GLStreamTextureImage() override {}