Add support for indexeddb sync in webworker

src/vector/indexedbd-worker.js

@@ -0,0 +1,26 @@
+/*
+Copyright 2017 Vector Creations Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// The prescribed way of doing this import would be:
+//import {IndexedDbStoreWorker} from 'matrix-js-sdk';
+// However, this still pulls in all of the js-sdk and we only use a tiny fraction
+// of it. It also causes an Olm error to appear because we don't have an Olm in scope.
+// Instead, we do this:
+import IndexedDbStoreWorker from 'matrix-js-sdk/lib/store/indexeddb-remote-worker';
+
+const remoteWorker = new IndexedDbStoreWorker(postMessage);
+
+onmessage = remoteWorker.onMessage;