Fix use after free bug by calling GetTokenService in Core's ctor.

sync/internal_api/attachments/attachment_downloader.cc

Index: sync/internal_api/attachments/attachment_downloader.cc
diff --git a/sync/internal_api/attachments/attachment_downloader.cc b/sync/internal_api/attachments/attachment_downloader.cc
index d9adc226cb9081b7de7a85604f25332a483c03fd..a3c780f648ad063c24250da6a1c846bdc7e1a710 100644
--- a/sync/internal_api/attachments/attachment_downloader.cc
+++ b/sync/internal_api/attachments/attachment_downloader.cc
@@ -20,14 +20,14 @@ scoped_ptr<AttachmentDownloader> AttachmentDownloader::Create(
         url_request_context_getter,
     const std::string& account_id,
     const OAuth2TokenService::ScopeSet scopes,
-    scoped_ptr<OAuth2TokenServiceRequest::TokenServiceProvider>
+    const scoped_refptr<OAuth2TokenServiceRequest::TokenServiceProvider>&
         token_service_provider) {
   return scoped_ptr<AttachmentDownloader>(
       new AttachmentDownloaderImpl(sync_service_url,
                                    url_request_context_getter,
                                    account_id,
                                    scopes,
-                                   token_service_provider.Pass()));
+                                   token_service_provider));
 }
 
 }  // namespace syncer