views: use darker stroke for non-prominent buttons

ui/views/controls/button/md_text_button.cc

Index: ui/views/controls/button/md_text_button.cc
diff --git a/ui/views/controls/button/md_text_button.cc b/ui/views/controls/button/md_text_button.cc
index 9b3d05986a6469e9d7ec436c6575f13065149d8d..8bf7749284942b66e60698ffae3377900d189a92 100644
--- a/ui/views/controls/button/md_text_button.cc
+++ b/ui/views/controls/button/md_text_button.cc
@@ -271,7 +271,7 @@ void MdTextButton::UpdateColors() {
   }
 
   SkColor stroke_color =
-      is_prominent_ ? SK_ColorTRANSPARENT : SkColorSetA(text_color, 0x33);
+      is_prominent_ ? SK_ColorTRANSPARENT : SkColorSetA(text_color, 0x4e);

[Evan Stade, 2016/10/12 15:28:35]

perhaps a note about how this was calculated or what it means? Something like:

// The spec specifies black with 0x33 alpha for the default stroke. Here we
derive it from the text color: 0x4e with ChromeIconGrey is very close.

[Elly Fong-Jones, 2016/10/12 17:46:46]

Done.

   DCHECK_EQ(SK_AlphaOPAQUE, static_cast<int>(SkColorGetA(bg_color)));
   set_background(Background::CreateBackgroundPainter(
       true, Painter::CreateRoundRectWith1PxBorderPainter(