Clean up CF To NS Casts and make them slightly safer

ui/gfx/canvas_skia_mac.mm

Index: ui/gfx/canvas_skia_mac.mm
diff --git a/ui/gfx/canvas_skia_mac.mm b/ui/gfx/canvas_skia_mac.mm
index c82e1aae3e8eb17bd17f614caf1a728327ee8306..7e9b03461c8fb308d1ee06fc4f0e1c4490bf80ab 100644
--- a/ui/gfx/canvas_skia_mac.mm
+++ b/ui/gfx/canvas_skia_mac.mm
@@ -6,6 +6,7 @@
 
 #include "ui/gfx/canvas_skia.h"
 
+#include "base/mac_util.h"
 #include "base/mac/scoped_cftyperef.h"
 #include "base/sys_string_conversions.h"
 #include "third_party/skia/include/core/SkShader.h"
@@ -72,7 +73,7 @@ void CanvasSkia::DrawStringInt(const string16& text,
                                        attributes:attributes] autorelease];
   base::mac::ScopedCFTypeRef<CTFramesetterRef> framesetter(
       CTFramesetterCreateWithAttributedString(
-      reinterpret_cast<CFAttributedStringRef>(ns_string)));
+          base::mac::NSToCFCast(ns_string)));
 
   CGRect text_bounds = CGRectMake(x, y, w, h);
   CGMutablePathRef path = CGPathCreateMutable();