add default webrtc trackers when there is webrtc support and global.W…

…EBTORRENT_ANNOUNCE is not defined

fix #672

lib/torrent.js

@@ -30,6 +30,8 @@ var Swarm = require('bittorrent-swarm')
 var uniq = require('uniq')
 var ut_metadata = require('ut_metadata')
 var ut_pex = require('ut_pex') // browser exclude
+var Peer = require('simple-peer')
+var createTorrent = require('create-torrent')
 
 var File = require('./file')
 var RarityMap = require('./rarity-map')
@@ -50,6 +52,16 @@ var TMP = typeof pathExists.sync === 'function'
   ? path.join(pathExists.sync('/tmp') ? '/tmp' : os.tmpDir(), 'webtorrent')
   : '/tmp/webtorrent'
 
+if (Peer.WEBRTC_SUPPORT && !global.WEBTORRENT_ANNOUNCE) {
+  global.WEBTORRENT_ANNOUNCE = createTorrent.announceList
+    .map(function (arr) {
+      return arr[0]
+    })
+    .filter(function (url) {
+      return url.indexOf('wss://') === 0 || url.indexOf('ws://') === 0
+    })
+}
+
 inherits(Torrent, EventEmitter)
 
 /**