Clean up CF To NS Casts and make them slightly safer

ui/gfx/canvas_skia_mac.mm

 // Copyright (c) 2010 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.
 
 #import <Cocoa/Cocoa.h>
 
 #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"
 #include "ui/gfx/font.h"
 #include "ui/gfx/rect.h"
 
 namespace gfx {
 
 CanvasSkia::CanvasSkia(int width, int height, bool is_opaque)
     : skia::PlatformCanvas(width, height, is_opaque) {
@@ skipping 46 matching lines @@
           font.GetNativeFont(), NSFontAttributeName,
           ns_color, NSForegroundColorAttributeName,
           ns_style, NSParagraphStyleAttributeName,
           nil];
 
   NSAttributedString* ns_string =
       [[[NSAttributedString alloc] initWithString:base::SysUTF16ToNSString(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();
   CGPathAddRect(path, NULL, text_bounds);
 
   base::mac::ScopedCFTypeRef<CTFrameRef> frame(
       CTFramesetterCreateFrame(framesetter, CFRangeMake(0, 0), path, NULL));
   CTFrameDraw(frame, context);
   CGContextRestoreGState(context);
   endPlatformPaint();
 }
 
 }  // namespace gfx