Revert of Convert //net and //chromecast to std::unordered_*

net/base/platform_mime_util_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.
 
 #include "net/base/platform_mime_util.h"
 
 #import <Foundation/Foundation.h>
 
 #include <string>
 
@@ skipping 55 matching lines @@
       UTTypeCopyPreferredTagWithClass(uti, kUTTagClassFilenameExtension));
   if (!ext_ref)
     return false;
 
   *ext = base::SysCFStringRefToUTF8(ext_ref);
   return true;
 }
 
 void PlatformMimeUtil::GetPlatformExtensionsForMimeType(
     const std::string& mime_type,
-    std::unordered_set<base::FilePath::StringType>* extensions) const {
+    base::hash_set<base::FilePath::StringType>* extensions) const {
 #if defined(OS_IOS)
   NSArray* extensions_list = nil;
 #else
   // There is no API for this that uses UTIs. The WebKitSystemInterface call
   // WKGetExtensionsForMIMEType() is a thin wrapper around
   // [[NSURLFileTypeMappings sharedMappings] extensionsForMIMEType:], which is
   // used by Firefox as well.
   //
   // See:
   // http://mxr.mozilla.org/mozilla-central/search?string=extensionsForMIMEType
   // http://www.openradar.me/11384153
   // rdar://11384153
   NSArray* extensions_list =
       [[NSURLFileTypeMappings sharedMappings]
           extensionsForMIMEType:base::SysUTF8ToNSString(mime_type)];
 #endif  // defined(OS_IOS)
 
   if (extensions_list) {
     for (NSString* extension in extensions_list)
       extensions->insert(base::SysNSStringToUTF8(extension));
   } else {
     // Huh? Give up.
     base::FilePath::StringType ext;
     if (GetPreferredExtensionForMimeType(mime_type, &ext))
       extensions->insert(ext);
   }
 }
 
 }  // namespace net