MacViews: Claim -[NSView isOpaque] for the content view according to the root layer properties.

ui/views/cocoa/bridged_content_view.mm

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ui/views/cocoa/bridged_content_view.h"
 
 #include "base/logging.h"
 #import "base/mac/mac_util.h"
 #import "base/mac/scoped_nsobject.h"
 #include "base/strings/sys_string_conversions.h"
@@ skipping 643 matching lines @@
 
   // If there's a layer, painting occurs in BridgedNativeWidget::OnPaintLayer().
   if (hostedView_->GetWidget()->GetLayer())
     return;
 
   gfx::CanvasSkiaPaint canvas(dirtyRect, false /* opaque */);
   hostedView_->GetWidget()->OnNativeWidgetPaint(
       ui::CanvasPainter(&canvas, 1.f).context());
 }
 
+- (BOOL)isOpaque {
+  if (!hostedView_)
+    return NO;
+
+  ui::Layer* layer = hostedView_->GetWidget()->GetLayer();
+  return layer && layer->fills_bounds_opaquely();
+}
+
 // To maximize consistency with the Cocoa browser (mac_views_browser=0), accept
 // mouse clicks immediately so that clicking on Chrome from an inactive window
 // will allow the event to be processed, rather than merely activate the window.
 - (BOOL)acceptsFirstMouse:(NSEvent*)theEvent {
   return YES;
 }
 
 // NSDraggingDestination protocol overrides.
 
 - (NSDragOperation)draggingEntered:(id<NSDraggingInfo>)sender {
@@ skipping 627 matching lines @@
   }
 
   return [super accessibilityAttributeValue:attribute];
 }
 
 - (id)accessibilityHitTest:(NSPoint)point {
   return [hostedView_->GetNativeViewAccessible() accessibilityHitTest:point];
 }
 
 @end