[SyncFS] Handle dirty tracker IDs in MetadataDatabaseIndexOnDisk

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 10c2856e722cfb803fd277a3a3862c47036212e9..7a53bc58c351e19e815d2bc10bad935bb74542d7 100644
--- a/chrome/browser/sync_file_system/drive_backend/metadata_database.cc
+++ b/chrome/browser/sync_file_system/drive_backend/metadata_database.cc
@@ -43,6 +43,8 @@ namespace drive_backend {
 
 namespace {
 
+void EmptyStatusCallback(SyncStatusCode status) {}
+
 std::string FileKindToString(FileKind file_kind) {
   switch (file_kind) {
     case FILE_KIND_UNSUPPORTED:
@@ -1367,12 +1369,16 @@ MetadataDatabase::ActivationStatus MetadataDatabase::TryActivateTracker(
 
 void MetadataDatabase::LowerTrackerPriority(int64 tracker_id) {
   DCHECK(worker_sequence_checker_.CalledOnValidSequencedThread());
-  index_->DemoteDirtyTracker(tracker_id);
+  scoped_ptr<leveldb::WriteBatch> batch(new leveldb::WriteBatch);
+  index_->DemoteDirtyTracker(tracker_id, batch.get());
+  WriteToDatabase(batch.Pass(), base::Bind(&EmptyStatusCallback));

[tzik, 2014/07/07 14:28:47]

I think consecutive call of this function will make the database inconsistent.
Since index class tries to read a data from the database before WriteToDatabase
completion.
Not necessary in this CL, but it's time to make WriteToDatabase() synchronous.

[peria, 2014/07/08 03:05:07]

Add a TODO comment on WriteToDatabase().

 }
 
 void MetadataDatabase::PromoteLowerPriorityTrackersToNormal() {
   DCHECK(worker_sequence_checker_.CalledOnValidSequencedThread());
-  index_->PromoteDemotedDirtyTrackers();
+  scoped_ptr<leveldb::WriteBatch> batch(new leveldb::WriteBatch);
+  index_->PromoteDemotedDirtyTrackers(batch.get());
+  WriteToDatabase(batch.Pass(), base::Bind(&EmptyStatusCallback));
 }
 
 bool MetadataDatabase::GetNormalPriorityDirtyTracker(