Maintain minimal error response.

content/browser/renderer_host/render_widget_host_view_aura.cc

Index: content/browser/renderer_host/render_widget_host_view_aura.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_aura.cc b/content/browser/renderer_host/render_widget_host_view_aura.cc
index fd85fcc8745cdf59c93e87322518bda129aff961..92e1b535773baba95d396342266e9576a886af57 100644
--- a/content/browser/renderer_host/render_widget_host_view_aura.cc
+++ b/content/browser/renderer_host/render_widget_host_view_aura.cc
@@ -1064,9 +1064,9 @@ void RenderWidgetHostViewAura::CopyFromCompositingSurface(
     const gfx::Rect& src_subrect,
     const gfx::Size& dst_size,
     ReadbackRequestCallback& callback,
-    const SkColorType color_type) {
+    const SkColorType preferred_color_type) {
   delegated_frame_host_->CopyFromCompositingSurface(
-      src_subrect, dst_size, callback, color_type);
+      src_subrect, dst_size, callback, preferred_color_type);
 }
 
 void RenderWidgetHostViewAura::CopyFromCompositingSurfaceToVideoFrame(
@@ -2685,10 +2685,6 @@ void RenderWidgetHostViewAura::ForwardKeyboardEvent(
   host_->ForwardKeyboardEvent(event);
 }
 
-SkColorType RenderWidgetHostViewAura::PreferredReadbackFormat() {
-  return kN32_SkColorType;
-}
-
 ////////////////////////////////////////////////////////////////////////////////
 // DelegatedFrameHost, public: