[content] Fix background color update handling in RWHVAura.

content/browser/renderer_host/render_widget_host_view_mac.mm

Index: content/browser/renderer_host/render_widget_host_view_mac.mm
diff --git a/content/browser/renderer_host/render_widget_host_view_mac.mm b/content/browser/renderer_host/render_widget_host_view_mac.mm
index 2b0a11d2a17b90d248e7fd40e21649042cd28697..6ea1ed045892f45e5bb6db5c6f51826c3fd2aebf 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac.mm
+++ b/content/browser/renderer_host/render_widget_host_view_mac.mm
@@ -449,6 +449,7 @@ RenderWidgetHostViewMac::RenderWidgetHostViewMac(RenderWidgetHost* widget,
       is_guest_view_hack_(is_guest_view_hack),
       fullscreen_parent_host_view_(nullptr),
       needs_flush_input_(false),
+      background_color_(SK_ColorWHITE),
       weak_factory_(this) {
   // |cocoa_view_| owns us and we will be deleted when |cocoa_view_|
   // goes away.  Since we autorelease it, our caller must put
@@ -1644,9 +1645,11 @@ void RenderWidgetHostViewMac::ShowDefinitionForSelection() {
 void RenderWidgetHostViewMac::SetBackgroundColor(SkColor color) {
   if (color == background_color_)
     return;
+  background_color_ = color;
 
-  RenderWidgetHostViewBase::SetBackgroundColor(color);
-  bool opaque = GetBackgroundOpaque();
+  DCHECK(SkColorGetA(color) == SK_AlphaOPAQUE ||
+         SkColorGetA(color) == SK_AlphaTRANSPARENT);
+  bool opaque = SkColorGetA(color) == SK_AlphaOPAQUE;
 
   if (render_widget_host_)
     render_widget_host_->SetBackgroundOpaque(opaque);
@@ -1661,6 +1664,10 @@ void RenderWidgetHostViewMac::SetBackgroundColor(SkColor color) {
   [background_layer_ setBackgroundColor:cg_color];
 }
 
+SkColor RenderWidgetHostViewMac::background_color() const {
+  return background_color_;
+}
+
 BrowserAccessibilityManager*
     RenderWidgetHostViewMac::CreateBrowserAccessibilityManager(
         BrowserAccessibilityDelegate* delegate, bool for_root_frame) {