ui/gfx: remove redundant 32x32 DashedRect drawing if a dest rect is empty

ui/gfx/canvas.cc

Index: ui/gfx/canvas.cc
diff --git a/ui/gfx/canvas.cc b/ui/gfx/canvas.cc
index db8b28fc0a95d78aac894b8956ebc60651f68e69..e8d6a9166fb1136c5d94fca30912b80f137a01be 100644
--- a/ui/gfx/canvas.cc
+++ b/ui/gfx/canvas.cc
@@ -131,6 +131,8 @@ ImageSkiaRep Canvas::ExtractImageRep() const {
 }
 
 void Canvas::DrawDashedRect(const Rect& rect, SkColor color) {
+  if (rect.IsEmpty())
+    return;
   // Create a 2D bitmap containing alternating on/off pixels - we do this
   // so that you never get two pixels of the same color around the edges
   // of the focus rect (this may mean that opposing edges of the rect may