views: refactor away PlatformStyle::BackgroundColorForMdButton

chrome/browser/ui/libgtk2ui/native_theme_gtk2.cc

Index: chrome/browser/ui/libgtk2ui/native_theme_gtk2.cc
diff --git a/chrome/browser/ui/libgtk2ui/native_theme_gtk2.cc b/chrome/browser/ui/libgtk2ui/native_theme_gtk2.cc
index bc03083b34101e26f5daec027a74687b1e5d1aa1..7e8811976df7dc57039822d3e9d8d72b919ab3f0 100644
--- a/chrome/browser/ui/libgtk2ui/native_theme_gtk2.cc
+++ b/chrome/browser/ui/libgtk2ui/native_theme_gtk2.cc
@@ -329,6 +329,8 @@ SkColor NativeThemeGtk2::GetSystemColor(ColorId color_id) const {
       return GetSystemColor(kColorId_LinkEnabled);
     case kColorId_TextOnCallToActionColor:
       return GetTextColor(GetLabel(), SELECTED);
+    case kColorId_ButtonPressedShade:
+      return SK_ColorTRANSPARENT;
 
     // Textfield
     case kColorId_TextfieldDefaultColor: