views: use darker stroke for non-prominent buttons

ui/native_theme/native_theme_dark_aura.cc

Index: ui/native_theme/native_theme_dark_aura.cc
diff --git a/ui/native_theme/native_theme_dark_aura.cc b/ui/native_theme/native_theme_dark_aura.cc
index f40f64c654bd48061b9941c4b791d450a093a2c8..eacb1a6536d6c82d70eae15b5b2f6555c910d5bf 100644
--- a/ui/native_theme/native_theme_dark_aura.cc
+++ b/ui/native_theme/native_theme_dark_aura.cc
@@ -42,6 +42,10 @@ SkColor NativeThemeDarkAura::GetSystemColor(ColorId color_id) const {
       return kButtonEnabledColor;
     case kColorId_ProminentButtonColor:
       return gfx::kGoogleBlue300;
+    case kColorId_ProminentButtonBorderColor:
+      return SK_ColorTRANSPARENT;
+    case kColorId_NonProminentButtonBorderColor:
+      return SK_ColorWHITE;
 
     // Label
     case kColorId_LabelEnabledColor: