Show message if screen sharing start failed for arbitrary reason.

Fall back to legacy screen sharing when possible and inline install failed.

static/js/directives/screenshare.js

@@ -177,6 +177,7 @@ define(['jquery', 'underscore', 'text!partials/screenshare.html', 'text!partials
 					}
 				}, function(err) {
 					console.log("Screen sharing request returned error", err);
+					alertify.dialog.alert(translation._("Failed to start screen sharing (%s).", err));
 					$scope.stopScreenshare();
 				});
 

static/js/services/screensharing.js

@@ -130,6 +130,7 @@ define(['underscore', 'webrtc.adapter'], function(_) {
 				this.supported = this.autoinstall = true;
 				var that = this;
 				var waiting = false;
+				var prepareAlternative = this.prepare;
 				this.prepare = function(options) {
 					var d = $q.defer();
 					var install = chromeExtension.autoinstall.install();
@@ -167,8 +168,18 @@ define(['underscore', 'webrtc.adapter'], function(_) {
 							d.reject("Timeout while waiting for extension getting installed");
 						}, 30000);
 					}, function(err) {
+						console.log("Auto install of extension failed.", err);
+						if (prepareAlternative) {
+							var alternative = prepareAlternative(options);
+							alternative.then(function(id) {
+								d.resolve(id);
+							}, function() {
 								d.reject(err);
 							});
+						} else {
+							d.reject(err);
+						}
+					});
 					return d.promise;
 				};
 				this.cancel = function() {