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

chrome/browser/sync/engine/syncapi.h

Index: chrome/browser/sync/engine/syncapi.h
diff --git a/chrome/browser/sync/engine/syncapi.h b/chrome/browser/sync/engine/syncapi.h
index 7ccbe03eea445045ebcfce4a49c6d1336779b633..693dca91bba1dbaf22cfe5e7d8496122e250bda2 100644
--- a/chrome/browser/sync/engine/syncapi.h
+++ b/chrome/browser/sync/engine/syncapi.h
@@ -736,6 +736,14 @@ class SyncManager {
     // 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