views: use darker stroke for non-prominent buttons

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 24 matching lines @@
     case kColorId_WindowBackground:
     case kColorId_DialogBackground:
     case kColorId_BubbleBackground:
       return SK_ColorBLACK;
 
     // Button
     case kColorId_ButtonEnabledColor:
       return kButtonEnabledColor;
     case kColorId_ProminentButtonColor:
       return gfx::kGoogleBlue300;
+    case kColorId_ProminentButtonBorderColor:
+      return SK_ColorTRANSPARENT;
+    case kColorId_NonProminentButtonBorderColor:
+      return SK_ColorWHITE;
 
     // Label
     case kColorId_LabelEnabledColor:
       return kPrimaryTextColor;
 
     // Link
     case kColorId_LinkEnabled:
     case kColorId_LinkPressed:
       return gfx::kGoogleBlue300;
 
@@ skipping 94 matching lines @@
 
   NOTREACHED();
   return gfx::kPlaceholderColor;
 }
 
 NativeThemeDarkAura::NativeThemeDarkAura() {}
 
 NativeThemeDarkAura::~NativeThemeDarkAura() {}
 
 }  // namespace ui