Add information about sync session and other useful data to about:sync.

chrome/browser/sync/engine/syncapi.h

 // Copyright (c) 2011 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.
 
 // This file defines the "sync API", an interface to the syncer
 // backend that exposes (1) the core functionality of maintaining a consistent
 // local snapshot of a hierarchical object set; (2) a means to transactionally
 // access and modify those objects; (3) a means to control client/server
 // synchronization tasks, namely: pushing local object modifications to a
 // server, pulling nonlocal object modifications from a server to this client,
@@ skipping 718 matching lines @@
     // Total updates received by the syncer since browser start.
     int updates_received;
 
     // Of updates_received, how many were tombstones.
     int tombstone_updates_received;
     bool disk_full;
 
     // Total number of overwrites due to conflict resolver since browser start.
     int num_local_overwrites_total;
     int num_server_overwrites_total;
+
+    // Count of empty and non empty getupdates;
+    int nonempty_get_updates;
+    int empty_get_updates;
+
+    // Count of useless and useful syncs we perform.
+    int useless_sync_cycles;
+    int useful_sync_cycles;
   };
 
   // An interface the embedding application implements to receive notifications
   // from the SyncManager.  Register an observer via SyncManager::AddObserver.
   // This observer is an event driven model as the events may be raised from
   // different internal threads, and simply providing an "OnStatusChanged" type
   // notification complicates things such as trying to determine "what changed",
   // if different members of the Status object are modified from different
   // threads.  This way, the event is explicit, and it is safe for the Observer
   // to dispatch to a native thread or synchronize accordingly.
@@ skipping 282 matching lines @@
  private:
   // An opaque pointer to the nested private class.
   SyncInternal* data_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncManager);
 };
 
 }  // namespace sync_api
 
 #endif  // CHROME_BROWSER_SYNC_ENGINE_SYNCAPI_H_