Set root resource ID upon full feed update.

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 374 matching lines @@
   // Should be created from the file browser extension API on UI thread.
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 }
 
 void DriveFileSystem::Initialize() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   drive_service_->Initialize(profile_);
 
   resource_metadata_.reset(new DriveResourceMetadata);
+  if (!google_apis::util::IsDriveV2ApiEnabled())
+    resource_metadata_->InitializeRootEntry(kWAPIRootDirectoryResourceId);
+  // If Drive API is enabled, the root directory is initialized after
+  // About resource is obtained.
   feed_loader_.reset(new DriveFeedLoader(resource_metadata_.get(),
                                          drive_service_,
                                          webapps_registry_,
                                          cache_,
                                          blocking_task_runner_));
   feed_loader_->AddObserver(this);
 
   // Allocate the drive operation handlers.
   drive_operations_.Init(drive_service_,
                          this,  // DriveFileSystemInterface
@@ skipping 2135 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