Convert string16 to base::string16 in content.

content/common/mac/font_descriptor.mm

 // Copyright (c) 2011 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 "content/common/mac/font_descriptor.h"
 
 #include <Cocoa/Cocoa.h>
 
 #include "base/strings/sys_string_conversions.h"
 
 FontDescriptor::FontDescriptor(NSFont* font) {
   font_name = base::SysNSStringToUTF16([font fontName]);
   font_point_size = [font pointSize];
 }
 
-FontDescriptor::FontDescriptor(string16 name, float size) {
+FontDescriptor::FontDescriptor(base::string16 name, float size) {
   font_name = name;
   font_point_size = size;
 }
 
 NSFont* FontDescriptor::ToNSFont() const {
   NSString* font_name_ns = base::SysUTF16ToNSString(font_name);
   NSFont* font = [NSFont fontWithName:font_name_ns size:font_point_size];
   return font;
 }