Add NSString category for providing iOS6-style string drawing APIs.

ui/gfx/text_utils_ios.mm

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/text_utils.h"
 
 #import <UIKit/UIKit.h>
 
 #include <cmath>
 
 #include "base/strings/sys_string_conversions.h"
 #include "ui/gfx/font_list.h"
+#include "ui/ios/NSString+CrStringDrawing.h"
 
 namespace gfx {
 
 int GetStringWidth(const base::string16& text, const FontList& font_list) {
   return std::ceil(GetStringWidthF(text, font_list));
 }
 
 float GetStringWidthF(const base::string16& text, const FontList& font_list) {
   NSString* ns_text = base::SysUTF16ToNSString(text);
   NativeFont native_font = font_list.GetPrimaryFont().GetNativeFont();
-  if (!native_font)
-    return 0;
-  NSDictionary* attributes = @{ NSFontAttributeName : native_font };
-  return std::ceil([ns_text sizeWithAttributes:attributes].width);
+  return [ns_text cr_sizeWithFont:native_font].width;
 }
 
 }  // namespace gfx