Maintain minimal error response.

content/browser/frame_host/render_widget_host_view_child_frame.cc

Index: content/browser/frame_host/render_widget_host_view_child_frame.cc
diff --git a/content/browser/frame_host/render_widget_host_view_child_frame.cc b/content/browser/frame_host/render_widget_host_view_child_frame.cc
index ebbea17c2a927c70d7ad24f782b1946d61e31fdc..e39a642b3767802bd87148183d8b1749fd5e47e8 100644
--- a/content/browser/frame_host/render_widget_host_view_child_frame.cc
+++ b/content/browser/frame_host/render_widget_host_view_child_frame.cc
@@ -262,8 +262,8 @@ void RenderWidgetHostViewChildFrame::CopyFromCompositingSurface(
     const gfx::Rect& src_subrect,
     const gfx::Size& /* dst_size */,
     ReadbackRequestCallback& callback,
-    const SkColorType color_type) {
-  callback.Run(SkBitmap(), READBACK_NOT_SUPPORTED);
+    const SkColorType preferred_color_type) {
+  callback.Run(SkBitmap(), READBACK_FAILED);
 }
 
 void RenderWidgetHostViewChildFrame::CopyFromCompositingSurfaceToVideoFrame(
@@ -298,10 +298,6 @@ gfx::NativeViewId RenderWidgetHostViewChildFrame::GetParentForWindowlessPlugin()
 }
 #endif // defined(OS_WIN)
 
-SkColorType RenderWidgetHostViewChildFrame::PreferredReadbackFormat() {
-  return kN32_SkColorType;
-}
-
 BrowserAccessibilityManager*
 RenderWidgetHostViewChildFrame::CreateBrowserAccessibilityManager(
     BrowserAccessibilityDelegate* delegate) {