[SyncFileSystem] Add MetadataDatabase::TryNoSideEffectActivation

chrome/browser/sync_file_system/drive_backend/metadata_database.h

Index: chrome/browser/sync_file_system/drive_backend/metadata_database.h
diff --git a/chrome/browser/sync_file_system/drive_backend/metadata_database.h b/chrome/browser/sync_file_system/drive_backend/metadata_database.h
index 2a54d85096cc801025fb42f71bab58a5e56d4091..c1b38e8a8cd5119e073fc549f222b29f1d4500b3 100644
--- a/chrome/browser/sync_file_system/drive_backend/metadata_database.h
+++ b/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();