Convert string16 to base::string16 in content.

content/browser/web_contents/web_drag_dest_mac.mm

 // Copyright (c) 2012 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 "content/browser/web_contents/web_drag_dest_mac.h"
 
 #import <Carbon/Carbon.h>
 
 #include "base/strings/sys_string_conversions.h"
 #include "content/browser/renderer_host/render_view_host_impl.h"
@@ skipping 272 matching lines @@
   if ([types containsObject:NSFilenamesPboardType]) {
     NSArray* files = [pboard propertyListForType:NSFilenamesPboardType];
     if ([files isKindOfClass:[NSArray class]] && [files count]) {
       for (NSUInteger i = 0; i < [files count]; i++) {
         NSString* filename = [files objectAtIndex:i];
         BOOL exists = [[NSFileManager defaultManager]
                            fileExistsAtPath:filename];
         if (exists) {
           data->filenames.push_back(
               DropData::FileInfo(
-                  base::SysNSStringToUTF16(filename), string16()));
+                  base::SysNSStringToUTF16(filename), base::string16()));
         }
       }
     }
   }
 
   // TODO(pinkerton): Get file contents. http://crbug.com/34661
 
   // Get custom MIME data.
   if ([types containsObject:ui::kWebCustomDataPboardType]) {
     NSData* customData = [pboard dataForType:ui::kWebCustomDataPboardType];
     ui::ReadCustomDataIntoMap([customData bytes],
                               [customData length],
                               &data->custom_data);
   }
 }
 
 @end