views: use darker stroke for non-prominent buttons

ui/views/controls/button/md_text_button.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/views/controls/button/md_text_button.h"
 
 #include "base/i18n/case_conversion.h"
 #include "ui/base/material_design/material_design_controller.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/color_palette.h"
@@ skipping 252 matching lines @@
       bg_color = color_utils::BlendTowardOppositeLuma(
           bg_color, gfx::kDisabledControlAlpha);
   }
 
   if (state() == STATE_PRESSED) {
     SkColor shade =
         theme->GetSystemColor(ui::NativeTheme::kColorId_ButtonPressedShade);
     bg_color = color_utils::GetResultingPaintColor(shade, bg_color);
   }
 
+  // Specified text color: 5a5a5a @ 1.0 alpha
+  // Specified stroke color: 000000 @ 0.2 alpha
+  // 000000 @ 0.2 is very close to 5a5a5a @ 0.308 (== 0x4e); both are cccccc @
+  // 1.0, and this way if NativeTheme changes the button color, the button
+  // stroke will also change colors to match.
   SkColor stroke_color =
-      is_prominent_ ? SK_ColorTRANSPARENT : SkColorSetA(text_color, 0x33);
+      is_prominent_ ? SK_ColorTRANSPARENT : SkColorSetA(text_color, 0x4e);
   DCHECK_EQ(SK_AlphaOPAQUE, static_cast<int>(SkColorGetA(bg_color)));
   set_background(Background::CreateBackgroundPainter(
       true, Painter::CreateRoundRectWith1PxBorderPainter(
                 bg_color, stroke_color, kInkDropSmallCornerRadius)));
 }
 
 }  // namespace views