[SyncFS] Retry initialization of MetadataDatabase on failure of loading ServiceMetadata

chrome/browser/sync_file_system/drive_backend/metadata_database.cc

Index: chrome/browser/sync_file_system/drive_backend/metadata_database.cc
diff --git a/chrome/browser/sync_file_system/drive_backend/metadata_database.cc b/chrome/browser/sync_file_system/drive_backend/metadata_database.cc
index 5456f52593ce52a28506f67bb25842de016b11d9..80499480f47f966c23d8f2d3700adb12dcd515a8 100644
--- a/chrome/browser/sync_file_system/drive_backend/metadata_database.cc
+++ b/chrome/browser/sync_file_system/drive_backend/metadata_database.cc
@@ -1428,7 +1428,8 @@ void MetadataDatabase::CreateOnWorkerTaskRunner(
   if (status != SYNC_STATUS_OK)
     metadata_database.reset();
 
-  metadata_database->DetachFromSequence();
+  if (metadata_database)
+    metadata_database->DetachFromSequence();
   create_param->worker_task_runner->PostTask(
       FROM_HERE,
       base::Bind(
@@ -1460,6 +1461,15 @@ SyncStatusCode MetadataDatabase::Initialize() {
   } else {
     index_ = MetadataDatabaseIndex::Create(db_.get());
   }
+  if (!index_) {
+    // Delete all entries in |db_| to reset it.
+    scoped_ptr<LevelDBWrapper::Iterator> itr = db_->NewIterator();
+    for (itr->SeekToFirst(); itr->Valid();)
+      itr->Delete();

[nhiroki, 2014/09/02 08:36:25]

Although not related to this CL and you don't have to address now, how about
renaming 'Delete()' to 'DeleteAndAdvance()' or something else? At first I was a
bit confused at this iteration because nobody calls itr->Next()...

[peria, 2014/09/03 04:08:13]

Acknowledged.

+    db_->Commit();

[nhiroki, 2014/09/02 07:26:04]

If you want to delete all records, can you use leveldb::DestroyDB() to avoid a
full scan?

[peria, 2014/09/02 07:36:27]

We have to update LevelDBWrapper class to use it :(
Will do in another patch.

[nhiroki, 2014/09/02 08:36:25]

Okay, can we have a TODO comment about that?

[peria, 2014/09/03 04:08:13]

Done.

+
+    return SYNC_DATABASE_ERROR_FAILED;

[nhiroki, 2014/09/02 07:26:04]

Let me confirm... this makes the SyncFS disabled until reloading the app. Is
this right?

[peria, 2014/09/02 07:36:27]

Yes, it is.
We have to run SyncEngineInitializer again.

[nhiroki, 2014/09/02 08:36:25]

I see... there would be another option to retry the initialization from here
(either is ok to me).

[peria, 2014/09/03 04:08:13]

Acknowledged.

+  }
 
   status = LevelDBStatusToSyncStatusCode(db_->Commit());
   if (status != SYNC_STATUS_OK)