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

ui/gfx/text_utils_ios.mm

Index: ui/gfx/text_utils_ios.mm
diff --git a/ui/gfx/text_utils_ios.mm b/ui/gfx/text_utils_ios.mm
index e687f3545474d46f90927510ca173735ed07175d..c6b8570239caea2143531c91051b6e369f0abaf2 100644
--- a/ui/gfx/text_utils_ios.mm
+++ b/ui/gfx/text_utils_ios.mm
@@ -10,6 +10,7 @@
 
 #include "base/strings/sys_string_conversions.h"
 #include "ui/gfx/font_list.h"
+#include "ui/ios/NSString+CrStringDrawing.h"
 
 namespace gfx {
 
@@ -20,10 +21,7 @@ int GetStringWidth(const base::string16& text, const FontList& 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