Abort sync cycles when download step fails

sync/engine/sync_scheduler.h

Index: sync/engine/sync_scheduler.h
diff --git a/sync/engine/sync_scheduler.h b/sync/engine/sync_scheduler.h
index d5ff4c0a44522a1223f4be14e9118b5313c491f9..4ec621d77b45c72bbb4c13c992234b5cea4f4ced 100644
--- a/sync/engine/sync_scheduler.h
+++ b/sync/engine/sync_scheduler.h
@@ -179,6 +179,7 @@ class SyncScheduler : public sessions::SyncSession::Delegate {
   };
   friend class SyncSchedulerTest;
   friend class SyncSchedulerWhiteboxTest;
+  friend class SyncerTest;
 
   FRIEND_TEST_ALL_PREFIXES(SyncSchedulerWhiteboxTest,
       DropNudgeWhileExponentialBackOff);
@@ -247,6 +248,12 @@ class SyncScheduler : public sessions::SyncSession::Delegate {
 
   static const char* GetDecisionString(JobProcessDecision decision);
 
+  // Assign |start| and |end| to appropriate SyncerStep values for the
+  // specified |purpose|.
+  static void SetSyncerStepsForPurpose(
+      SyncSessionJob::SyncSessionJobPurpose purpose,
+      SyncerStep* start, SyncerStep* end);
+
   // Helpers that log before posting to |sync_loop_|.  These will only post
   // the task in between calls to Start/Stop.
   void PostTask(const tracked_objects::Location& from_here,
@@ -340,12 +347,6 @@ class SyncScheduler : public sessions::SyncSession::Delegate {
   // Creates a session for a poll and performs the sync.
   void PollTimerCallback();
 
-  // Assign |start| and |end| to appropriate SyncerStep values for the
-  // specified |purpose|.
-  void SetSyncerStepsForPurpose(SyncSessionJob::SyncSessionJobPurpose purpose,
-                                SyncerStep* start,
-                                SyncerStep* end);
-
   // Used to update |connection_code_|, see below.
   void UpdateServerConnectionManagerStatus(
       HttpResponse::ServerConnectionCode code);