Fix a bug that unmounting devices on the policy update can be a busy loop.

chrome/browser/chromeos/file_manager/fake_disk_mount_manager.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 "chrome/browser/chromeos/file_manager/fake_disk_mount_manager.h"
 
 #include "base/callback.h"
 #include "base/stl_util.h"
 
 namespace file_manager {
@@ skipping 89 matching lines @@
 
   MountPointMap::iterator iter = mount_points_.find(mount_path);
   if (iter == mount_points_.end())
     return;
   const MountPointInfo mount_point = iter->second;
   mount_points_.erase(iter);
   FOR_EACH_OBSERVER(DiskMountManager::Observer, observers_,
                     OnMountEvent(DiskMountManager::UNMOUNTING,
                                  chromeos::MOUNT_ERROR_NONE,
                                  mount_point));
-  // Currently |callback| is just ignored.
+  // Enqueue callback so that |FakeDiskMountManager::FinishAllUnmountRequest()|
+  // can call them.
+  pending_unmount_callbacks_.push(callback);

[fukino, 2016/09/16 07:31:34]

Why do we need FinishAllUnmountPathRequests() called?
Is it possible to call each pending callbacks asynchronously without
FinishAllUnmountPathRequest()?

[yamaguchi, 2016/09/16 08:49:51]

The main purpose of this change in the test & the fake class is to detect the
bug with the original code.
If we combine the test with the existing code, it will form an infinite loop
(and will crash by overflow) because just calling the UnmountPath function does
not finish unmount right away.
("synchronous" here means to finish call in sync with the invocation of
UnmountPath,)

+}
+
+bool FakeDiskMountManager::FinishAllUnmountPathRequests() {
+  if (pending_unmount_callbacks_.empty())
+    return false;
+  while (!pending_unmount_callbacks_.empty()) {
+    pending_unmount_callbacks_.front().Run(chromeos::MOUNT_ERROR_NONE);
+    pending_unmount_callbacks_.pop();
+  }
+  return true;
 }
 
 void FakeDiskMountManager::FormatMountedDevice(const std::string& mount_path) {
 }
 
 void FakeDiskMountManager::UnmountDeviceRecursively(
     const std::string& device_path,
     const UnmountDeviceRecursivelyCallbackType& callback) {
 }
 
 bool FakeDiskMountManager::AddDiskForTest(Disk* disk) {
   DCHECK(disk);
   return disks_.insert(make_pair(disk->device_path(), disk)).second;
 }
 
 bool FakeDiskMountManager::AddMountPointForTest(
     const MountPointInfo& mount_point) {
   return false;
 }
 
 void FakeDiskMountManager::InvokeDiskEventForTest(
     chromeos::disks::DiskMountManager::DiskEvent event,
     const chromeos::disks::DiskMountManager::Disk* disk) {
   FOR_EACH_OBSERVER(chromeos::disks::DiskMountManager::Observer,
                     observers_,
                     OnDiskEvent(event, disk));
 }
 
 }  // namespace file_manager