[Mac] Allow vibrancy & transparency on WebContentsView

content/browser/renderer_host/render_widget_host_view_mac.mm

 // Copyright (c) 2012 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.
 
 #include "content/browser/renderer_host/render_widget_host_view_mac.h"
 
 #import <objc/runtime.h>
 #include <OpenGL/gl.h>
 #include <QuartzCore/QuartzCore.h>
 
@@ skipping 1690 matching lines @@
 
 - (id)initWithRenderWidgetHostViewMac:(RenderWidgetHostViewMac*)r {
   self = [super initWithFrame:NSZeroRect];
   if (self) {
     self.acceptsTouchEvents = YES;
     editCommand_helper_.reset(new RenderWidgetHostViewMacEditCommandHelper);
     editCommand_helper_->AddEditingSelectorsToClass([self class]);
 
     renderWidgetHostView_.reset(r);
     canBeKeyView_ = YES;
+    opaque_ = YES;
     focusedPluginIdentifier_ = -1;
 
     // OpenGL support:
     if ([self respondsToSelector:
         @selector(setWantsBestResolutionOpenGLSurface:)]) {
       [self setWantsBestResolutionOpenGLSurface:YES];
     }
     [[NSNotificationCenter defaultCenter]
         addObserver:self
            selector:@selector(didChangeScreenParameters:)
@@ skipping 68 matching lines @@
 }
 
 - (BOOL)acceptsFirstMouse:(NSEvent*)theEvent {
   return [self acceptsMouseEventsWhenInactive];
 }
 
 - (void)setCloseOnDeactivate:(BOOL)b {
   closeOnDeactivate_ = b;
 }
 
+- (void)setOpaque:(BOOL)opaque {
+  opaque_ = opaque;
+}
+
 - (BOOL)shouldIgnoreMouseEvent:(NSEvent*)theEvent {
   NSWindow* window = [self window];
   // If this is a background window, don't handle mouse movement events. This
   // is the expected behavior on the Mac as evidenced by other applications.
   if ([theEvent type] == NSMouseMoved &&
       ![self acceptsMouseEventsWhenInactive] &&
       ![window isKeyWindow]) {
     return YES;
   }
 
@@ skipping 1551 matching lines @@
   if (!string) return NO;
 
   // If the user is currently using an IME, confirm the IME input,
   // and then insert the text from the service, the same as TextEdit and Safari.
   [self confirmComposition];
   [self insertText:string];
   return YES;
 }
 
 - (BOOL)isOpaque {
-  return YES;
+  return opaque_;
 }
 
 // "-webkit-app-region: drag | no-drag" is implemented on Mac by excluding
 // regions that are not draggable. (See ControlRegionView in
 // native_app_window_cocoa.mm). This requires the render host view to be
 // draggable by default.
 - (BOOL)mouseDownCanMoveWindow {
   return YES;
 }
 
 @end