Add non-blocking sync code to ProfileSyncService

sync/internal_api/public/sync_manager.h

Index: sync/internal_api/public/sync_manager.h
diff --git a/sync/internal_api/public/sync_manager.h b/sync/internal_api/public/sync_manager.h
index 38bad0786d4983dfaaac7e23c680782c7d482183..32b6814791378a54719c4861e16894786a931088 100644
--- a/sync/internal_api/public/sync_manager.h
+++ b/sync/internal_api/public/sync_manager.h
@@ -333,7 +333,7 @@ class SYNC_EXPORT SyncManager : public syncer::InvalidationHandler {
   virtual UserShare* GetUserShare() = 0;
 
   // Returns an instance of the main interface for non-blocking sync types.
-  virtual syncer::SyncCore* GetSyncCore() = 0;
+  virtual base::WeakPtr<syncer::SyncCore> GetSyncCore() = 0;

[rlarocque, 2014/03/28 18:10:14]

In case you're wondering, I changed my mind on this when I realized that
sync_backend_host_core.h wasn't allowed to #include sync_core.h, and that I had
to return a WeakPtr here so I could forward declare it.

 
   // Returns the cache_guid of the currently open database.
   // Requires that the SyncManager be initialized.