sync: reland scheduler ownership refactoring, now with less crash

sync/engine/sync_scheduler_unittest.cc

Index: sync/engine/sync_scheduler_unittest.cc
diff --git a/sync/engine/sync_scheduler_unittest.cc b/sync/engine/sync_scheduler_unittest.cc
index 7746aea533eae49396d2eef9c104ae7eb2b1a729..20453f1aa95dcd23e42f37f45a5cab01d92dbbf4 100644
--- a/sync/engine/sync_scheduler_unittest.cc
+++ b/sync/engine/sync_scheduler_unittest.cc
@@ -1133,4 +1133,32 @@ TEST_F(SyncSchedulerTest, StartWhenNotConnected) {
   MessageLoop::current()->RunAllPending();
 }
 
+TEST_F(SyncSchedulerTest, ServerConnectionChangeDuringBackoff) {
+  UseMockDelayProvider();
+  EXPECT_CALL(*delay(), GetDelay(_))
+      .WillRepeatedly(Return(TimeDelta::FromMilliseconds(0)));
+
+  StartSyncScheduler(SyncScheduler::NORMAL_MODE);
+  connection()->SetServerNotReachable();
+  connection()->UpdateConnectionStatus();
+
+  EXPECT_CALL(*syncer(), SyncShare(_,_,_))
+    .WillOnce(DoAll(Invoke(sessions::test_util::SimulateConnectionFailure),
+                    Return(true)))
+    .WillOnce(DoAll(Invoke(sessions::test_util::SimulateSuccess),
+                    QuitLoopNowAction()));
+
+  scheduler()->ScheduleNudgeAsync(
+      zero(), NUDGE_SOURCE_LOCAL, ModelTypeSet(BOOKMARKS), FROM_HERE);
+
+  PumpLoop();  // Run the nudge, that will fail and schedule a quick retry.
+  ASSERT_TRUE(scheduler()->IsBackingOff());
+
+  // Before we run the scheduled canary, trigger a server connection change.
+  connection()->SetServerReachable();
+  connection()->UpdateConnectionStatus();
+  scheduler()->OnConnectionStatusChange();
+  MessageLoop::current()->RunAllPending();
+}
+
 }  // namespace syncer