Try to get rid of all direct references to particular native themes.

ui/native_theme/native_theme_dark_aura.cc

 // Copyright 2015 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 "ui/native_theme/native_theme_dark_aura.h"
 
 #include "ui/gfx/color_palette.h"
 
 namespace ui {
 
@@ skipping 133 matching lines @@
     case kColorId_ThrobberWaitingColor:
     case kColorId_ThrobberLightColor:
     case kColorId_NumColors:
       return gfx::kPlaceholderColor;
   }
 
   NOTREACHED();
   return gfx::kPlaceholderColor;
 }
 
-NativeThemeDarkAura::NativeThemeDarkAura() {}
+NativeThemeDarkAura::NativeThemeDarkAura() : NativeThemeAura(false) {}
 
 NativeThemeDarkAura::~NativeThemeDarkAura() {}
 
 }  // namespace ui