views: use darker stroke for non-prominent buttons

ui/native_theme/common_theme.cc

Index: ui/native_theme/common_theme.cc
diff --git a/ui/native_theme/common_theme.cc b/ui/native_theme/common_theme.cc
index 69c0602befe74dc32553b51d37349efea993a7be..91b90562c5f2b52b2aa48f39ea251dc253ef8c38 100644
--- a/ui/native_theme/common_theme.cc
+++ b/ui/native_theme/common_theme.cc
@@ -161,6 +161,10 @@ SkColor GetAuraColor(NativeTheme::ColorId color_id,
       return SK_ColorTRANSPARENT;
     case NativeTheme::kColorId_ButtonDisabledColor:
       return kDisabledMenuItemForegroundColor;
+    case NativeTheme::kColorId_ProminentButtonBorderColor:
+      return SK_ColorTRANSPARENT;
+    case NativeTheme::kColorId_NonProminentButtonBorderColor:
+      return SkColorSetA(SK_ColorBLACK, 0x33);
 
     // MenuItem
     case NativeTheme::kColorId_SelectedMenuItemForegroundColor: