Initialize root resource ID only once for Drive API.

chrome/browser/chromeos/drive/drive_feed_loader.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_feed_loader.h"
 
 #include <set>
 
 #include "base/command_line.h"
 #include "base/file_util.h"
@@ skipping 363 matching lines @@
   if (feed_data.get())
     about_resource = gdata::AboutResource::CreateFrom(*feed_data);
 
   if (!about_resource.get()) {
     LoadFromServer(params.Pass());
     return;
   }
 
   bool changes_detected = true;
   int64 largest_changestamp = about_resource->largest_change_id();
-  resource_metadata_->InitializeRootEntry(about_resource->root_folder_id());
+
+  // Initialize the root entry only for the first time.
+  if (resource_metadata_->root_resource_id().empty())
+    resource_metadata_->InitializeRootEntry(about_resource->root_folder_id());
 
   if (local_changestamp >= largest_changestamp) {
     if (local_changestamp > largest_changestamp) {
       LOG(WARNING) << "Cached client feed is fresher than server, client = "
                    << local_changestamp
                    << ", server = "
                    << largest_changestamp;
     }
     // If our cache holds the latest state from the server, change the
     // state to FROM_SERVER.
@@ skipping 518 matching lines @@
         dir_iter != changed_dirs.end(); ++dir_iter) {
       FOR_EACH_OBSERVER(DriveFeedLoaderObserver, observers_,
                         OnDirectoryChanged(*dir_iter));
     }
   }
 
   return error;
 }
 
 }  // namespace drive