sync: Add pre-commit update avoidance mode + flag

sync/sessions/data_type_tracker.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // A class to track the per-type scheduling data.
 #ifndef SYNC_SESSIONS_DATA_TYPE_TRACKER_H_
 #define SYNC_SESSIONS_DATA_TYPE_TRACKER_H_
 
 #include <deque>
 #include <string>
@@ skipping 31 matching lines @@
   void RecordSuccessfulSyncCycle();
 
   // Updates the size of the invalidations payload buffer.
   void UpdatePayloadBufferSize(size_t new_size);
 
   // Returns true if there is a good reason to perform a sync cycle.  This does
   // not take into account whether or not now is a good time to perform a sync
   // 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;
 
   // Returns true if we've received an invalidation since we last fetched
   // updates.
   bool HasPendingInvalidation() const;
 
   // Returns the most recent invalidation payload.
   std::string GetMostRecentInvalidationPayload() const;
 
@@ skipping 46 matching lines @@
 
   // If !unthrottle_time_.is_null(), this type is throttled and may not download
   // or commit data until the specified time.
   base::TimeTicks unthrottle_time_;
 };
 
 }  // namespace syncer
 }  // namespace sessions
 
 #endif  // SYNC_SESSIONS_DATA_TYPE_TRACKER_H_