sync: Gracefully handle very early shutdown

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 e0ea9a80f884fc006a72a4cb9f8bffc1c8cbca26..01cbdd72d429829bbd9fd73221ea719af00b1b21 100644
--- a/sync/engine/sync_scheduler_unittest.cc
+++ b/sync/engine/sync_scheduler_unittest.cc
@@ -41,6 +41,7 @@ using sync_pb::GetUpdatesCallerInfo;
 
 class MockSyncer : public Syncer {
  public:
+  MockSyncer();
   MOCK_METHOD3(NormalSyncShare, bool(ModelTypeSet,
                                      const sessions::NudgeTracker&,
                                      sessions::SyncSession*));
@@ -51,6 +52,9 @@ class MockSyncer : public Syncer {
   MOCK_METHOD2(PollSyncShare, bool(ModelTypeSet, sessions::SyncSession*));
 };
 
+MockSyncer::MockSyncer()
+  : Syncer(NULL) {}
+
 typedef std::vector<TimeTicks> SyncShareTimes;
 
 void QuitLoopNow() {