Revert of Make cc/paint have concrete types

ash/common/shelf/overflow_button.cc

Index: ash/common/shelf/overflow_button.cc
diff --git a/ash/common/shelf/overflow_button.cc b/ash/common/shelf/overflow_button.cc
index b254012be91dc3c8b99cad84147d9f3910e21060..ccb585c6cc785a7fed087df58d843866e2ff6f2b 100644
--- a/ash/common/shelf/overflow_button.cc
+++ b/ash/common/shelf/overflow_button.cc
@@ -100,7 +100,7 @@
 void OverflowButton::PaintBackground(gfx::Canvas* canvas,
                                      const gfx::Rect& bounds) {
   cc::PaintFlags flags;
-  flags.setAntiAlias(true);
+  flags.setFlags(cc::PaintFlags::kAntiAlias_Flag);
   flags.setColor(background_color_);
   canvas->DrawRoundRect(bounds, kOverflowButtonCornerRadius, flags);
 }