Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/chromeos/drive/drive_file_system.cc

 // 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 "chrome/browser/chromeos/drive/drive_file_system.h"
 
 #include "base/bind.h"
 #include "base/file_util.h"
 #include "base/json/json_file_value_serializer.h"
 #include "base/message_loop_proxy.h"
@@ skipping 2163 matching lines @@
 
 DriveFileSystemMetadata DriveFileSystem::GetMetadata() const {
   DriveFileSystemMetadata metadata;
   metadata.largest_changestamp = resource_metadata_->largest_changestamp();
   metadata.origin = ContentOriginToString(resource_metadata_->origin());
   if (feed_loader_->refreshing())
     metadata.origin += " (refreshing)";
   return metadata;
 }
 
-void DriveFileSystem::Observe(int type,
-                              const content::NotificationSource& source,
-                              const content::NotificationDetails& details) {
+void DriveFileSystem::OnPreferenceChanged(PrefServiceBase* service,
+                                          const std::string& pref_name) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  DCHECK(pref_name == prefs::kDisableDriveHostedFiles);
 
-  if (type == chrome::NOTIFICATION_PREF_CHANGED) {
-    PrefService* pref_service = profile_->GetPrefs();
-    std::string* pref_name = content::Details<std::string>(details).ptr();
-    if (*pref_name == prefs::kDisableDriveHostedFiles) {
-      SetHideHostedDocuments(
-          pref_service->GetBoolean(prefs::kDisableDriveHostedFiles));
-    }
-  } else {
-    NOTREACHED();
-  }
+  PrefService* pref_service = profile_->GetPrefs();
+  SetHideHostedDocuments(
+      pref_service->GetBoolean(prefs::kDisableDriveHostedFiles));
 }
 
 void DriveFileSystem::SetHideHostedDocuments(bool hide) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   if (hide == hide_hosted_docs_)
     return;
 
   hide_hosted_docs_ = hide;
   const FilePath root_path = resource_metadata_->root()->GetFilePath();
@@ skipping 336 matching lines @@
     return;
   }
 
   PlatformFileInfoProto entry_file_info;
   DriveEntry::ConvertPlatformFileInfoToProto(*file_info, &entry_file_info);
   *entry_proto->mutable_file_info() = entry_file_info;
   callback.Run(DRIVE_FILE_OK, entry_proto.Pass());
 }
 
 }  // namespace drive