Revert 222154 "sync: Gracefully handle very early shutdown"

trunk/src/sync/engine/syncer.h

Index: trunk/src/sync/engine/syncer.h
===================================================================
--- trunk/src/sync/engine/syncer.h	(revision 222204)
+++ trunk/src/sync/engine/syncer.h	(working copy)
@@ -21,8 +21,6 @@
 
 namespace syncer {
 
-class CancelationSignal;
-
 // A Syncer provides a control interface for driving the individual steps
 // of the sync cycle.  Each cycle (hopefully) moves the client into closer
 // synchronization with the server.  The individual steps are modeled
@@ -37,10 +35,13 @@
  public:
   typedef std::vector<int64> UnsyncedMetaHandles;
 
-  Syncer(CancelationSignal* cancelation_signal);
+  Syncer();
   virtual ~Syncer();
 
+  // Called by other threads to tell the syncer to stop what it's doing
+  // and return early from SyncShare, if possible.
   bool ExitRequested();
+  void RequestEarlyExit();
 
   // Fetches and applies updates, resolves conflicts and commits local changes
   // for |request_types| as necessary until client and server states are in
@@ -78,7 +79,8 @@
       sessions::SyncSession* session,
       sync_pb::GetUpdatesCallerInfo::GetUpdatesSource source);
 
-  syncer::CancelationSignal* const cancelation_signal_;
+  bool early_exit_requested_;
+  base::Lock early_exit_requested_lock_;
 
   friend class SyncerTest;
   FRIEND_TEST_ALL_PREFIXES(SyncerTest, NameClashWithResolver);