Revert of Revert of Add mechanism to auto mount file systems in response to a URL request.

content/public/test/test_file_system_backend.cc

 // Copyright 2013 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/public/test/test_file_system_backend.h"
 
 #include <set>
 #include <string>
 #include <vector>
 
@@ skipping 119 matching lines @@
     return &update_observers_;
   }
 
   virtual const fileapi::ChangeObserverList* GetChangeObservers(
       FileSystemType type) const OVERRIDE {
     return &change_observers_;
   }
 
   virtual const fileapi::AccessObserverList* GetAccessObservers(
       FileSystemType type) const OVERRIDE {
-    NOTIMPLEMENTED();
     return NULL;
   }
 
   // FileUpdateObserver overrides.
   virtual void OnStartUpdate(const FileSystemURL& url) OVERRIDE {}
   virtual void OnUpdate(const FileSystemURL& url, int64 delta) OVERRIDE {
     usage_ += delta;
   }
   virtual void OnEndUpdate(const FileSystemURL& url) OVERRIDE {}
 
@@ skipping 107 matching lines @@
   return quota_util_->GetUpdateObservers(type);
 }
 
 void TestFileSystemBackend::AddFileChangeObserver(
     fileapi::FileChangeObserver* observer) {
   quota_util_->AddFileChangeObserver(
       fileapi::kFileSystemTypeTest, observer, quota_util_->task_runner());
 }
 
 }  // namespace content