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

ui/views/controls/combobox/combobox.cc

Index: ui/views/controls/combobox/combobox.cc
diff --git a/ui/views/controls/combobox/combobox.cc b/ui/views/controls/combobox/combobox.cc
index bb8623a26f631e183c6b62289581e95a1336fc19..e72f4b8c37fbfd0a86681409c8310495474365f4 100644
--- a/ui/views/controls/combobox/combobox.cc
+++ b/ui/views/controls/combobox/combobox.cc
@@ -833,10 +833,8 @@ void Combobox::PaintText(gfx::Canvas* canvas) {
     SkPaint paint;
     SkColor arrow_color = GetNativeTheme()->GetSystemColor(
         ui::NativeTheme::kColorId_ButtonEnabledColor);
-    // TODO(estade): share this disabled alpha value with other places that use
-    // it.
     if (!enabled())
-      arrow_color = SkColorSetA(arrow_color, 0x61);
+      arrow_color = SkColorSetA(arrow_color, gfx::kDisabledControlAlpha);
     paint.setColor(arrow_color);
     paint.setAntiAlias(true);
     canvas->DrawPath(path, paint);