fix(simple_abr_manager): check for existance of addEventListener and …

…removeEventListener in navigator.connection before using them

fixes shaka-project#4542

lib/abr/simple_abr_manager.js

@@ -52,7 +52,7 @@ shaka.abr.SimpleAbrManager = class {
     // retrieving information about a user's network connection. We listen
     // to the change event to be able to make quick changes in case the type
     // of connectivity changes.
-    if (navigator.connection) {
+    if (navigator.connection && navigator.connection.addEventListener) {
       this.onNetworkInformationChange_ = () => {
         if (this.config_.useNetworkInformation && this.enabled_) {
           this.bandwidthEstimator_ = new shaka.abr.EwmaBandwidthEstimator();
@@ -143,7 +143,7 @@ shaka.abr.SimpleAbrManager = class {
   release() {
     // stop() should already have been called for unload
 
-    if (navigator.connection) {
+    if (navigator.connection && navigator.connection.removeEventListener) {
       navigator.connection.removeEventListener(
           'change', this.onNetworkInformationChange_);
       this.onNetworkInformationChange_ = null;