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

sync/engine/sync_scheduler_whitebox_unittest.cc

 // 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.
 
 #include "base/message_loop.h"
 #include "base/time.h"
 #include "sync/engine/backoff_delay_provider.h"
 #include "sync/engine/sync_scheduler_impl.h"
 #include "sync/engine/throttled_data_type_tracker.h"
 #include "sync/internal_api/public/engine/polling_constants.h"
@@ skipping 54 matching lines @@
 
   virtual void TearDown() {
     scheduler_.reset();
   }
 
   void SetMode(SyncScheduler::Mode mode) {
     scheduler_->mode_ = mode;
   }
 
   void SetLastSyncedTime(base::TimeTicks ticks) {
-    scheduler_->last_sync_session_end_time_ = ticks;
+    scheduler_->last_nudge_or_poll_end_time_ = ticks;
   }
 
   void ResetWaitInterval() {
     scheduler_->wait_interval_.reset();
   }
 
   void SetWaitIntervalToThrottled() {
     scheduler_->wait_interval_.reset(new SyncSchedulerImpl::WaitInterval(
         SyncSchedulerImpl::WaitInterval::THROTTLED, TimeDelta::FromSeconds(1)));
   }
@@ skipping 181 matching lines @@
   struct SyncSchedulerImpl::SyncSessionJob job;
   job.purpose = SyncSchedulerImpl::SyncSessionJob::CONFIGURATION;
   job.scheduled_start = TimeTicks::Now();
   job.is_canary_job = true;
   SyncSchedulerImpl::JobProcessDecision decision = DecideOnJob(job);
 
   EXPECT_EQ(decision, SyncSchedulerImpl::CONTINUE);
 }
 
 }  // namespace syncer