Maintain minimal error response.

content/browser/renderer_host/render_widget_host_view_mac.h

Index: content/browser/renderer_host/render_widget_host_view_mac.h
diff --git a/content/browser/renderer_host/render_widget_host_view_mac.h b/content/browser/renderer_host/render_widget_host_view_mac.h
index f29fcefcb40dc9942eb66a96c0175dc914b8086f..74bb9a004bc2895ddedd14f614873b047c3bcde4 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac.h
+++ b/content/browser/renderer_host/render_widget_host_view_mac.h
@@ -316,7 +316,7 @@ class CONTENT_EXPORT RenderWidgetHostViewMac
   void CopyFromCompositingSurface(const gfx::Rect& src_subrect,
                                   const gfx::Size& dst_size,
                                   ReadbackRequestCallback& callback,
-                                  SkColorType color_type) override;
+                                  SkColorType preferred_color_type) override;
   void CopyFromCompositingSurfaceToVideoFrame(
       const gfx::Rect& src_subrect,
       const scoped_refptr<media::VideoFrame>& target,
@@ -348,8 +348,6 @@ class CONTENT_EXPORT RenderWidgetHostViewMac
   // IPC::Sender implementation.
   bool Send(IPC::Message* message) override;
 
-  SkColorType PreferredReadbackFormat() override;
-
   // gfx::DisplayObserver implementation.
   void OnDisplayAdded(const gfx::Display& new_display) override;
   void OnDisplayRemoved(const gfx::Display& old_display) override;