Change AboutResourceLoader::GetAboutResource to wait for inflight update task.

chrome/browser/chromeos/drive/directory_loader.cc

 // 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.
 
 #include "chrome/browser/chromeos/drive/directory_loader.h"
 
 #include "base/callback.h"
 #include "base/callback_helpers.h"
 #include "base/metrics/histogram.h"
 #include "base/strings/string_number_conversions.h"
@@ skipping 280 matching lines @@
   const std::string& local_id = directory_fetch_info.local_id();
   ReadDirectoryCallbackState callback_state;
   callback_state.entries_callback = entries_callback;
   callback_state.completion_callback = completion_callback;
   pending_load_callback_[local_id].push_back(callback_state);
 
   // If loading task for |local_id| is already running, do nothing.
   if (pending_load_callback_[local_id].size() > 1)
     return;
 
-  // Note: To be precise, we need to call UpdateAboutResource() here. However,
-  // - It is costly to do GetAboutResource HTTP request every time.
-  // - The chance using an old value is small; it only happens when
-  //   ReadDirectory is called during one GetAboutResource roundtrip time
-  //   of a change list fetching.
-  // - Even if the value is old, it just marks the directory as older. It may
-  //   trigger one future unnecessary re-fetch, but it'll never lose data.
   about_resource_loader_->GetAboutResource(
       base::Bind(&DirectoryLoader::ReadDirectoryAfterGetAboutResource,
                  weak_ptr_factory_.GetWeakPtr(), local_id));
 }
 
 void DirectoryLoader::ReadDirectoryAfterLoadParent(
     const base::FilePath& directory_path,
     const ReadDirectoryEntriesCallback& entries_callback,
     const FileOperationCallback& completion_callback,
     FileError error) {
@@ skipping 250 matching lines @@
   // Also notify the observers.
   if (error == FILE_ERROR_OK && !directory_path->empty()) {
     FOR_EACH_OBSERVER(ChangeListLoaderObserver,
                       observers_,
                       OnDirectoryReloaded(*directory_path));
   }
 }
 
 }  // namespace internal
 }  // namespace drive