sync: Add pre-commit update avoidance mode + flag

sync/sessions/data_type_tracker.h

Index: sync/sessions/data_type_tracker.h
diff --git a/sync/sessions/data_type_tracker.h b/sync/sessions/data_type_tracker.h
index 6488f8e105de4b8e21fd289d849378c152da39b7..30bc3b6dbbc88f6b0c268caad00dc72338d35760 100644
--- a/sync/sessions/data_type_tracker.h
+++ b/sync/sessions/data_type_tracker.h
@@ -49,6 +49,10 @@ class DataTypeTracker {
   // cycle.  That's for the scheduler to decide.
   bool IsSyncRequired() const;
 
+  // Returns true if there is a good reason to fetch updates for this type as
+  // part of the next sync cycle.
+  bool IsGetUpdatesRequired() const;
+
   // Returns true if there is an uncommitted local change.
   bool HasLocalChangePending() const;