Share a common alpha value used for displaying disabled state in Harmony

ui/views/controls/button/toggle_button.cc

 // Copyright 2016 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/toggle_button.h"
 
 #include "third_party/skia/include/core/SkDrawLooper.h"
 #include "third_party/skia/include/core/SkPaint.h"
 #include "ui/gfx/canvas.h"
+#include "ui/gfx/color_palette.h"
 #include "ui/gfx/color_utils.h"
 #include "ui/views/animation/ink_drop_ripple.h"
 #include "ui/views/border.h"
 
 namespace views {
 
 namespace {
 
 // Constants are measured in dip.
 const int kTrackHeight = 12;
 const int kTrackWidth = 28;
 // Margins from edge of track to edge of view.
 const int kTrackVerticalMargin = 5;
 const int kTrackHorizontalMargin = 6;
 // Margin from edge of thumb to closest edge of view. Note that the thumb
 // margins must be sufficiently large to allow space for the shadow.
 const int kThumbHorizontalMargin = 4;
 // Margin from top/bottom edge of thumb to top/bottom edge of view.
 const int kThumbVerticalMargin = 3;
 
-// TODO(estade): get this color from the theme?
-const SkColor kTrackOffColor = SkColorSetA(SK_ColorBLACK, 0x61);
+// TODO(estade): get the base color (black) from the theme?
+const SkColor kTrackOffColor =
+    SkColorSetA(SK_ColorBLACK, gfx::kDisabledControlAlpha);
 
 }  // namespace
 
 ToggleButton::ToggleButton(ButtonListener* listener)
     : CustomButton(listener), is_on_(false), slide_animation_(this) {
   slide_animation_.SetSlideDuration(80 /* ms */);
   slide_animation_.SetTweenType(gfx::Tween::LINEAR);
   SetBorder(Border::CreateEmptyBorder(
       gfx::Insets(kTrackVerticalMargin, kTrackHorizontalMargin)));
   SetInkDropMode(InkDropMode::ON);
@@ skipping 94 matching lines @@
   thumb_bounds.set_x(thumb_bounds.x() +
                      slide_animation_.GetCurrentValue() *
                          (thumb_bounds.width() - thumb_bounds.height()));
   // The thumb is a circle, so the width should match the height.
   thumb_bounds.set_width(thumb_bounds.height());
   thumb_bounds.set_x(GetMirroredXForRect(thumb_bounds));
   return thumb_bounds;
 }
 
 }  // namespace views