Simulate transient error and verify exponential backoff.

chrome/browser/sync/engine/syncer.h

Index: chrome/browser/sync/engine/syncer.h
diff --git a/chrome/browser/sync/engine/syncer.h b/chrome/browser/sync/engine/syncer.h
index b333de72914b9037062a327fccf18d102c57ac8e..1de7dad6b73aa3203223452e3326de644c3157b6 100644
--- a/chrome/browser/sync/engine/syncer.h
+++ b/chrome/browser/sync/engine/syncer.h
@@ -87,6 +87,16 @@ class Syncer {
                          SyncerStep first_step,
                          SyncerStep last_step);
 
+  class ScopedSyncStartStopTracker {
+   public:
+    explicit ScopedSyncStartStopTracker(sessions::SyncSession* session);
+    ~ScopedSyncStartStopTracker();
+   private:
+    sessions::SyncSession* session_;
+
+    DISALLOW_COPY_AND_ASSIGN(ScopedSyncStartStopTracker);
+  };
+
  private:
   // Implements the PROCESS_CLIENT_COMMAND syncer step.
   void ProcessClientCommand(sessions::SyncSession* session);