sync: remove buggy freshness condition in SyncSchedulerImpl add defensive DCHECKs.

sync/engine/sync_scheduler_impl.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SYNC_ENGINE_SYNC_SCHEDULER_IMPL_H_
 #define SYNC_ENGINE_SYNC_SCHEDULER_IMPL_H_
 
+#include <map>
 #include <string>
 
 #include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/linked_ptr.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
 #include "base/time.h"
@@ skipping 253 matching lines @@
 
   // Used to update |connection_code_|, see below.
   void UpdateServerConnectionManagerStatus(
       HttpResponse::ServerConnectionCode code);
 
   // Called once the first time thread_ is started to broadcast an initial
   // session snapshot containing data like initial_sync_ended.  Important when
   // the client starts up and does not need to perform an initial sync.
   void SendInitialSnapshot();
 
+  // This is used for histogramming and analysis of ScheduleNudge* APIs.
+  // SyncScheduler is the ultimate choke-point for all such invocations (with
+  // and without InvalidationState variants, all NudgeSources, etc) and as such
+  // is the most flexible place to do this bookkeeping.
+  void UpdateNudgeTimeRecords(const sessions::SyncSourceInfo& info);
+
   virtual void OnActionableError(const sessions::SyncSessionSnapshot& snapshot);
 
   base::WeakPtrFactory<SyncSchedulerImpl> weak_ptr_factory_;
 
   // A second factory specially for weak_handle_this_, to allow the handle
   // to be const and alleviate threading concerns.
   base::WeakPtrFactory<SyncSchedulerImpl> weak_ptr_factory_for_weak_handle_;
 
   // For certain methods that need to worry about X-thread posting.
   const WeakHandle<SyncSchedulerImpl> weak_handle_this_;
@@ skipping 15 matching lines @@
 
   // Server-tweakable sessions commit delay.
   base::TimeDelta sessions_commit_delay_;
 
   // Periodic timer for polling.  See AdjustPolling.
   base::RepeatingTimer<SyncSchedulerImpl> poll_timer_;
 
   // The mode of operation.
   Mode mode_;
 
-  // TODO(tim): Bug 26339. This needs to track more than just time I think,
-  // since the nudges could be for different types. Current impl doesn't care.
-  base::TimeTicks last_sync_session_end_time_;
-
   // The latest connection code we got while trying to connect.
   HttpResponse::ServerConnectionCode connection_code_;
 
   // Tracks in-flight nudges so we can coalesce.
   scoped_ptr<SyncSessionJob> pending_nudge_;
 
   // Current wait state.  Null if we're not in backoff and not throttled.
   scoped_ptr<WaitInterval> wait_interval_;
 
   scoped_ptr<BackoffDelayProvider> delay_provider_;
 
   // Invoked to run through the sync cycle.
   scoped_ptr<Syncer> syncer_;
 
-  sessions::SyncSessionContext *session_context_;
+  sessions::SyncSessionContext* session_context_;
+
+  // A map tracking LOCAL NudgeSource invocations of ScheduleNudge* APIs,
+  // organized by datatype. Each datatype that was part of the types requested
+  // in the call will have its TimeTicks value updated.
+  typedef std::map<ModelType, base::TimeTicks> ModelTypeTimeMap;
+  ModelTypeTimeMap last_local_nudges_by_model_type_;
+
+  // Used as an "anti-reentrancy defensive assertion".
+  // While true, it is illegal for any new scheduling activity to take place.
+  // Ensures that higher layers don't break this law in response to events that
+  // take place during a sync cycle. We call this out because such violations
+  // could result in tight sync loops hitting sync servers.
+  bool no_scheduling_allowed_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncSchedulerImpl);
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_ENGINE_SYNC_SCHEDULER_IMPL_H_