Use a layer transform for the waiting throbber

ui/gfx/paint_throbber.h

Index: ui/gfx/paint_throbber.h
diff --git a/ui/gfx/paint_throbber.h b/ui/gfx/paint_throbber.h
index c4adab5dd2f35b5a6e078c7842655e76e7b06da1..fddfb4759f49d344c4992b45b80c945d7d79b60d 100644
--- a/ui/gfx/paint_throbber.h
+++ b/ui/gfx/paint_throbber.h
@@ -28,6 +28,12 @@ struct GFX_EXPORT ThrobberWaitingState {
   base::TimeDelta arc_time_offset;
 };
 
+GFX_EXPORT void PaintThrobberArc(Canvas* canvas,
+                                 const Rect& bounds,
+                                 SkColor color,
+                                 SkScalar start_angle,
+                                 SkScalar sweep);
+
 // Paints a single frame of the throbber in the "spinning", aka Material, state.
 GFX_EXPORT void PaintThrobberSpinning(Canvas* canvas,
     const Rect& bounds, SkColor color, const base::TimeDelta& elapsed_time);