Simulate transient error and verify exponential backoff.

chrome/test/live_sync/live_sync_test.h

Index: chrome/test/live_sync/live_sync_test.h
diff --git a/chrome/test/live_sync/live_sync_test.h b/chrome/test/live_sync/live_sync_test.h
index 0888fd4ba7ada463068e245f163cfc1c77c946bf..fc5e008155103a008aefcc0e55095098f0129664 100644
--- a/chrome/test/live_sync/live_sync_test.h
+++ b/chrome/test/live_sync/live_sync_test.h
@@ -142,6 +142,10 @@ class LiveSyncTest : public InProcessBrowserTest {
   // the server would return a birthday error on next sync.
   void TriggerBirthdayError();
 
+  // Triggers a transient error on the server. Note the server will stay in
+  // this state until shut down.
+  void TriggerTransientError();
+
  protected:
   // InProcessBrowserTest override. Destroys all the sync clients and sync
   // profiles created by a test.