Don't put a text shadow on blue buttons in gtk theme mode.

ui/native_theme/native_theme.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 UI_NATIVE_THEME_NATIVE_THEME_H_
 #define UI_NATIVE_THEME_NATIVE_THEME_H_
 
 #include "base/observer_list.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/native_widget_types.h"
@@ skipping 240 matching lines @@
     kColorId_ButtonBackgroundColor,
     kColorId_ButtonEnabledColor,
     kColorId_ButtonDisabledColor,
     kColorId_ButtonHighlightColor,
     kColorId_ButtonHoverColor,
     kColorId_ButtonHoverBackgroundColor,
     kColorId_BlueButtonEnabledColor,
     kColorId_BlueButtonDisabledColor,
     kColorId_BlueButtonPressedColor,
     kColorId_BlueButtonHoverColor,
+    kColorId_BlueButtonShadowColor,
     // MenuItem
     kColorId_EnabledMenuItemForegroundColor,
     kColorId_DisabledMenuItemForegroundColor,
     kColorId_DisabledEmphasizedMenuItemForegroundColor,
     kColorId_SelectedMenuItemForegroundColor,
     kColorId_FocusedMenuItemBackgroundColor,
     kColorId_HoverMenuItemBackgroundColor,
     kColorId_MenuSeparatorColor,
     kColorId_MenuBackgroundColor,
     kColorId_MenuBorderColor,
@@ skipping 78 matching lines @@
  private:
   // Observers to notify when the native theme changes.
   ObserverList<NativeThemeObserver> native_theme_observers_;
 
   DISALLOW_COPY_AND_ASSIGN(NativeTheme);
 };
 
 }  // namespace ui
 
 #endif  // UI_NATIVE_THEME_NATIVE_THEME_H_