[fsp] Add requestUnmount() method together with the request manager.

chrome/browser/chromeos/file_system_provider/observer.h

 // Copyright 2014 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.
 
 #ifndef CHROME_BROWSER_CHROMEOS_FILE_SYSTEM_PROVIDER_OBSERVER_H_
 #define CHROME_BROWSER_CHROMEOS_FILE_SYSTEM_PROVIDER_OBSERVER_H_
 
 #include <string>
 
+#include "base/files/file.h"
+
 namespace chromeos {
 namespace file_system_provider {
 
 class ProvidedFileSystem;
 
 // Observes file_system_provider::Service for mounting and unmounting events.
 class Observer {
  public:
-  // Called when a provided |file_system| is registered successfully.
-  virtual void OnProvidedFileSystemRegistered(
-      const ProvidedFileSystem& file_system) = 0;
+  // Called when a file system mounting has been invoked. For success, the
+  // |error| argument is set to FILE_OK. Otherwise, |error| contains a specific
+  // error code.
+  virtual void OnProvidedFileSystemMount(const ProvidedFileSystem& file_system,
+                                         base::File::Error error) = 0;
 
-  // Called when a provided |file_system| is unregistered successfully.
-  virtual void OnProvidedFileSystemUnregistered(
-      const ProvidedFileSystem& file_system) = 0;
+  // Called when a file system unmounting has been invoked. For success, the
+  // |error| argument is set to FILE_OK. Otherwise, |error| contains a specific
+  // error code.
+  virtual void OnProvidedFileSystemUnmount(
+      const ProvidedFileSystem& file_system,
+      base::File::Error error) = 0;
 };
 
 }  // namespace file_system_provider
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_FILE_SYSTEM_PROVIDER_OBSERVER_H_