Revert "Allow MessageFilters to restrict listening to specific message classes"

content/browser/mime_registry_message_filter.cc

 // 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/browser/mime_registry_message_filter.h"
 
 #include "content/common/mime_registry_messages.h"
 #include "net/base/mime_util.h"
 
 namespace content {
 
-MimeRegistryMessageFilter::MimeRegistryMessageFilter()
-    : BrowserMessageFilter(MimeRegistryMsgStart) {
+MimeRegistryMessageFilter::MimeRegistryMessageFilter() {
 }
 
 MimeRegistryMessageFilter::~MimeRegistryMessageFilter() {
 }
 
 void MimeRegistryMessageFilter::OverrideThreadForMessage(
     const IPC::Message& message,
     BrowserThread::ID* thread) {
   if (IPC_MESSAGE_CLASS(message) == MimeRegistryMsgStart)
     *thread = BrowserThread::FILE;
@@ skipping 16 matching lines @@
     const base::FilePath::StringType& ext, std::string* mime_type) {
   net::GetMimeTypeFromExtension(ext, mime_type);
 }
 
 void MimeRegistryMessageFilter::OnGetMimeTypeFromFile(
     const base::FilePath& file_path, std::string* mime_type) {
   net::GetMimeTypeFromFile(file_path, mime_type);
 }
 
 }  // namespace content