[SyncFileSystem] Add MetadataDatabase::TryNoSideEffectActivation

This is needed to handle create-create conflict of folders in LocalToRemoteSyncer.

BUG=240165
NOTRY=true

Review URL: https://codereview.chromium.org/99813005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238354 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/sync_file_system/drive_backend/metadata_database.cc

@@ -1041,6 +1041,25 @@ void MetadataDatabase::UpdateTracker(int64 tracker_id,
   WriteToDatabase(batch.Pass(), callback);
 }
 
+bool MetadataDatabase::TryNoSideEffectActivation(
+    int64 tracker_id,
+    const SyncStatusCallback& callback) {
+  DCHECK(ContainsKey(tracker_by_id_, tracker_id));
+  const FileTracker& tracker = *tracker_by_id_[tracker_id];
+  if (tracker.active()) {
+    RunSoon(FROM_HERE, base::Bind(callback, SYNC_STATUS_OK));
+    return true;
+  }
+
+  if (!CanActivateTracker(tracker))
+    return false;
+
+  scoped_ptr<leveldb::WriteBatch> batch(new leveldb::WriteBatch);
+  MakeTrackerActive(tracker_id, batch.get());
+  WriteToDatabase(batch.Pass(), callback);
+  return true;
+}
+
 void MetadataDatabase::LowerTrackerPriority(int64 tracker_id) {
   TrackerByID::const_iterator found = tracker_by_id_.find(tracker_id);
   if (found == tracker_by_id_.end())

chrome/browser/sync_file_system/drive_backend/metadata_database.h

@@ -273,6 +273,13 @@ class MetadataDatabase {
                      const FileDetails& updated_details,
                      const SyncStatusCallback& callback);
 
+  // Returns true if the tracker can be safely activated without deactivating
+  // any other trackers.  In this case, tries to activate the tracker, and
+  // invokes |callback| upon completion.
+  // Returns false otherwise.  In false case, |callback| will not be invoked.
+  bool TryNoSideEffectActivation(int64 tracker_id,
+                                 const SyncStatusCallback& callback);
+
   // Changes the priority of the tracker to low.
   void LowerTrackerPriority(int64 tracker_id);
   void PromoteLowerPriorityTrackersToNormal();