Support Olm with WebAssembly

wasm Olm has a new interface: it now has an init method that needs
to be called and the promise it returns waited on before the Olm
module is used. Support that, and allow Crypto etc to be imported
whether Olm is enabled or not. Change whether olm is enabled to
be async since now it will be unavailable if the async module init
fails. Don't call getOlmVersion() until the Olm.init() is done.

src/crypto/index.js

@@ -36,6 +36,12 @@ const DeviceList = require('./DeviceList').default;
 import OutgoingRoomKeyRequestManager from './OutgoingRoomKeyRequestManager';
 import IndexedDBCryptoStore from './store/indexeddb-crypto-store';
 
+const Olm = global.Olm;
+
+export function isCryptoAvailable() {
+    return Boolean(Olm);
+}
+
 /**
  * Cryptography bits
  *
@@ -62,7 +68,7 @@ import IndexedDBCryptoStore from './store/indexeddb-crypto-store';
  *
  * @param {RoomList} roomList An initialised RoomList object
  */
-function Crypto(baseApis, sessionStore, userId, deviceId,
+export default function Crypto(baseApis, sessionStore, userId, deviceId,
                 clientStore, cryptoStore, roomList) {
     this._baseApis = baseApis;
     this._sessionStore = sessionStore;
@@ -124,6 +130,10 @@ utils.inherits(Crypto, EventEmitter);
  * Returns a promise which resolves once the crypto module is ready for use.
  */
 Crypto.prototype.init = async function() {
+    // Olm is just an object with a .then, not a fully-fledged promise, so
+    // pass it into bluebird to make it a proper promise.
+    await Olm.init();
+
     const sessionStoreHasAccount = Boolean(this._sessionStore.getEndToEndAccount());
     let cryptoStoreHasAccount;
     await this._cryptoStore.doTxn(
@@ -1518,6 +1528,3 @@ class IncomingRoomKeyRequestCancellation {
  * @event module:client~MatrixClient#"crypto.warning"
  * @param {string} type One of the strings listed above
  */
-
-/** */
-module.exports = Crypto;