[Sync] Remove backend unrecoverable error handler

sync/syncable/directory.h

Index: sync/syncable/directory.h
diff --git a/sync/syncable/directory.h b/sync/syncable/directory.h
index 7358f179bd94e0a53fb97ecb69eb3ae30c4e8235..d71fcf8a0e3c50037ff9e1d019a6e0d3e435776b 100644
--- a/sync/syncable/directory.h
+++ b/sync/syncable/directory.h
@@ -248,11 +248,12 @@ class SYNC_EXPORT Directory {
   // Does not take ownership of |encryptor|.
   // |report_unrecoverable_error_function| may be NULL.
   // Takes ownership of |store|.
-  Directory(DirectoryBackingStore* store,
-            UnrecoverableErrorHandler* unrecoverable_error_handler,
-            const base::Closure& report_unrecoverable_error_function,
-            NigoriHandler* nigori_handler,
-            Cryptographer* cryptographer);
+  Directory(
+      DirectoryBackingStore* store,
+      const WeakHandle<UnrecoverableErrorHandler>& unrecoverable_error_handler,
+      const base::Closure& report_unrecoverable_error_function,
+      NigoriHandler* nigori_handler,
+      Cryptographer* cryptographer);
   virtual ~Directory();
 
   // Does not take ownership of |delegate|, which must not be NULL.
@@ -636,7 +637,7 @@ class SYNC_EXPORT Directory {
 
   scoped_ptr<DirectoryBackingStore> store_;
 
-  UnrecoverableErrorHandler* const unrecoverable_error_handler_;
+  const WeakHandle<UnrecoverableErrorHandler> unrecoverable_error_handler_;
   base::Closure report_unrecoverable_error_function_;
   bool unrecoverable_error_set_;