[Mac] Update tab audio icon to Material Design and tweak close box color.

chrome/browser/ui/cocoa/hover_close_button.h

 // 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.
 
 #ifndef CHROME_BROWSER_UI_COCOA_HOVER_CLOSE_BUTTON_H_
 #define CHROME_BROWSER_UI_COCOA_HOVER_CLOSE_BUTTON_H_
 
 #import <Cocoa/Cocoa.h>
 
+#include "third_party/skia/include/core/SkColor.h"
 #import "ui/base/cocoa/hover_button.h"
 
 @class GTMKeyValueAnimation;
 
 // The standard close button for our Mac UI which is the "x" that changes to a
 // dark circle with the "x" when you hover over it. Used to close tabs.
 @interface HoverCloseButton : HoverButton<NSAnimationDelegate> {
  @private
   GTMKeyValueAnimation* fadeOutAnimation_;
   HoverState previousState_;
 }
 
+// Returns the Material Design color of the "x".
+- (SkColor)iconColor;
 @end
 
 // A version of HoverCloseButton with the "x" icon changed to match the WebUI
 // look.
 @interface WebUIHoverCloseButton : HoverCloseButton
 @end
 
 #endif  // CHROME_BROWSER_UI_COCOA_HOVER_CLOSE_BUTTON_H_