Set root resource ID upon full feed update.

chrome/browser/chromeos/drive/drive_feed_loader.cc

Index: chrome/browser/chromeos/drive/drive_feed_loader.cc
diff --git a/chrome/browser/chromeos/drive/drive_feed_loader.cc b/chrome/browser/chromeos/drive/drive_feed_loader.cc
index f92a585b6648fb387d023170fad07a92c3a1ccf0..cafb94573a90ed5cc1cb3b17baa76eaececa9cc2 100644
--- a/chrome/browser/chromeos/drive/drive_feed_loader.cc
+++ b/chrome/browser/chromeos/drive/drive_feed_loader.cc
@@ -381,7 +381,10 @@ void DriveFeedLoader::OnGetAboutResource(
 
   bool changes_detected = true;
   int64 largest_changestamp = about_resource->largest_change_id();
-  resource_metadata_->InitializeRootEntry(about_resource->root_folder_id());
+
+  // Copy the root resource ID for use in UpdateFromFeed().
+  params->root_resource_id = about_resource->root_folder_id();
+  DCHECK(!params->root_resource_id.empty());
 
   if (local_changestamp >= largest_changestamp) {
     if (local_changestamp > largest_changestamp) {
@@ -494,7 +497,8 @@ void DriveFeedLoader::OnFeedFromServerLoaded(scoped_ptr<LoadFeedParams> params,
 
   UpdateFromFeed(params->feed_list,
                  params->start_changestamp,
-                 params->root_feed_changestamp);
+                 params->root_feed_changestamp,
+                 params->root_resource_id);
 
   // Save file system metadata to disk.
   SaveFileSystem();
@@ -887,12 +891,25 @@ void DriveFeedLoader::SaveFileSystem() {
 void DriveFeedLoader::UpdateFromFeed(
     const ScopedVector<google_apis::DocumentFeed>& feed_list,
     int64 start_changestamp,
-    int64 root_feed_changestamp) {
+    int64 root_feed_changestamp,
+    const std::string& root_resource_id) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   DVLOG(1) << "Updating directory with a feed";
 
   std::set<FilePath> changed_dirs;
 
+  if (start_changestamp == 0) {
+    // This is a full fetch and on full fetch the root has to be initialized
+    // before children are added by DriveFeedProcessor.
+    if (google_apis::util::IsDriveV2ApiEnabled()) {
+      DCHECK(!root_resource_id.empty());
+      resource_metadata_->SetRootResourceId(root_resource_id);
+    } else {
+      // Use fixed root resource ID for WAPI.
+      resource_metadata_->SetRootResourceId(kWAPIRootDirectoryResourceId);
+    }
+  }
+
   DriveFeedProcessor feed_processor(resource_metadata_);
   feed_processor.ApplyFeeds(
       feed_list,