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

chrome/browser/themes/theme_properties.h

 // Copyright (c) 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.
 
 #ifndef CHROME_BROWSER_THEMES_THEME_PROPERTIES_H_
 #define CHROME_BROWSER_THEMES_THEME_PROPERTIES_H_
 
 #include <set>
 #include <string>
 
@@ skipping 70 matching lines @@
     COLOR_CONTROL_BACKGROUND = 1000,
     COLOR_TOOLBAR_SEPARATOR,
 
     // These colors don't have constant default values. They are derived from
     // the runtime value of other colors.
     COLOR_NTP_SECTION_HEADER_TEXT,
     COLOR_NTP_SECTION_HEADER_TEXT_HOVER,
     COLOR_NTP_SECTION_HEADER_RULE,
     COLOR_NTP_SECTION_HEADER_RULE_LIGHT,
     COLOR_NTP_TEXT_LIGHT,
-    // Color for any icon on the tabstrip (e.g. media indicator).
-    COLOR_TAB_ICON,
     COLOR_THROBBER_SPINNING,
     COLOR_THROBBER_WAITING,
 #if defined(ENABLE_SUPERVISED_USERS)
     COLOR_SUPERVISED_USER_LABEL,
     COLOR_SUPERVISED_USER_LABEL_BACKGROUND,
     COLOR_SUPERVISED_USER_LABEL_BORDER,
 #endif
 
     COLOR_STATUS_BAR_TEXT,
 
@@ skipping 40 matching lines @@
 
   // Returns the default color for the given color |id| COLOR_* enum value.
   // Returns SK_ColorRED if |id| is invalid.
   static SkColor GetDefaultColor(int id);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(ThemeProperties);
 };
 
 #endif  // CHROME_BROWSER_THEMES_THEME_PROPERTIES_H_