sync: Make nudge + config jobs reliable in SyncerThread2

chrome/browser/sync/engine/syncer_thread2.h

Index: chrome/browser/sync/engine/syncer_thread2.h
diff --git a/chrome/browser/sync/engine/syncer_thread2.h b/chrome/browser/sync/engine/syncer_thread2.h
index 3fbdd7f26d437f92a98009ef33933bf9ef1050a4..4f86dc5aa4a90eac0b6c372ab6ca9c03eedd314b 100644
--- a/chrome/browser/sync/engine/syncer_thread2.h
+++ b/chrome/browser/sync/engine/syncer_thread2.h
@@ -43,6 +43,15 @@ class SyncerThread : public sessions::SyncSession::Delegate,
     NORMAL_MODE,
   };
 
+  enum JobProcessDecision {
+    // Indicates we should continue with the current job.
+    CONTINUE,
+    // Indicates that we should save it to be processed later.
+    SAVE,
+    // Indicates we should drop this job.
+    DROP,
+  };
+
   // Takes ownership of both |context| and |syncer|.
   SyncerThread(sessions::SyncSessionContext* context, Syncer* syncer);
   virtual ~SyncerThread();
@@ -161,22 +170,29 @@ class SyncerThread : public sessions::SyncSession::Delegate,
   // Helper to ScheduleNextSync in case of consecutive sync errors.
   void HandleConsecutiveContinuationError(const SyncSessionJob& old_job);
 
-  // Determines if it is legal to run a sync job for |purpose| at
-  // |scheduled_start|.  This checks current operational mode, backoff or
+  // Determines if it is legal to run a sync |job|.
+  // This checks current operational mode, backoff or
   // throttling, freshness (so we don't make redundant syncs), and connection.
-  bool ShouldRunJob(SyncSessionJobPurpose purpose,
-                    const base::TimeTicks& scheduled_start);
+  bool ShouldRunJob(const SyncSessionJob& job);
+
+  // Decide on whether to run, save or discard the job when we are in
+  // back off mode.
+  JobProcessDecision DecideOnJobWhileBackingOff(const SyncSessionJob& job);
+
+  // Decide whether we should run, save or discard the job.
+  JobProcessDecision ProcessJob(const SyncSessionJob& job);
 
   // 'Impl' here refers to real implementation of public functions, running on
   // |thread_|.
   void StartImpl(Mode mode, linked_ptr<ModeChangeCallback> callback);
   void ScheduleNudgeImpl(
       const base::TimeDelta& delay,
-      NudgeSource source,
+      sync_pb::GetUpdatesCallerInfo::GetUpdatesSource source,
       const syncable::ModelTypePayloadMap& types_with_payloads,
-      const tracked_objects::Location& nudge_location);
+      bool is_canary_job, const tracked_objects::Location& nudge_location);
   void ScheduleConfigImpl(const ModelSafeRoutingInfo& routing_info,
-                          const std::vector<ModelSafeWorker*>& workers);
+      const std::vector<ModelSafeWorker*>& workers,
+      const sync_pb::GetUpdatesCallerInfo::GetUpdatesSource source);
   void ScheduleClearUserDataImpl();
 
   // Returns true if the client is currently in exponential backoff.
@@ -243,6 +259,9 @@ class SyncerThread : public sessions::SyncSession::Delegate,
 
   scoped_ptr<sessions::SyncSessionContext> session_context_;
 
+  bool saved_nudge_;
+  sync_pb::GetUpdatesCallerInfo::GetUpdatesSource saved_source_;
+
   DISALLOW_COPY_AND_ASSIGN(SyncerThread);
 };