Render the tab close button as a vector-based icon.

chrome/browser/ui/cocoa/tabs/media_indicator_button_cocoa.mm

 // Copyright 2013 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 "chrome/browser/ui/cocoa/tabs/media_indicator_button_cocoa.h"
 
 #include "base/logging.h"
 #include "base/mac/foundation_util.h"
 #include "base/thread_task_runner_handle.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_view.h"
@@ skipping 59 matching lines @@
   fadeAnimation_.reset();
   [super removeFromSuperview];
 }
 
 - (void)transitionToMediaState:(TabMediaState)nextState {
   if (nextState == mediaState_)
     return;
 
   if (nextState != TAB_MEDIA_STATE_NONE) {
     [self
-        setImage:chrome::GetTabMediaIndicatorImage(nextState, nil).ToNSImage()];
+        setImage:chrome::GetTabMediaIndicatorImage(nextState, 0).ToNSImage()];
     affordanceImage_.reset(
-        [chrome::GetTabMediaIndicatorAffordanceImage(nextState, nil)
+        [chrome::GetTabMediaIndicatorAffordanceImage(nextState, 0)
                 .ToNSImage() retain]);
   }
 
   if ((mediaState_ == TAB_MEDIA_STATE_AUDIO_PLAYING &&
        nextState == TAB_MEDIA_STATE_AUDIO_MUTING) ||
       (mediaState_ == TAB_MEDIA_STATE_AUDIO_MUTING &&
        nextState == TAB_MEDIA_STATE_AUDIO_PLAYING) ||
       (mediaState_ == TAB_MEDIA_STATE_AUDIO_MUTING &&
        nextState == TAB_MEDIA_STATE_NONE)) {
     // Instant user feedback: No fade animation.
@@ skipping 137 matching lines @@
   if (enable && tabView && ([tabView state] != NSOnState)) {
     const int requiredWidth =
         NSWidth([self frame]) * kMinMouseSelectableAreaPercent / 100;
     enable = ([tabView widthOfLargestSelectableRegion] >= requiredWidth);
   }
 
   [self setEnabled:enable];
 }
 
 @end