Test that MediaRecorder.start() throws if MediaRecorder.stream is inactive.

Differential Revision: https://phabricator.services.mozilla.com/D41587

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1514158
gecko-commit: c60d1d4fe9f44743cbface9d892a6b04bce9106e
gecko-integration-branch: autoland
gecko-reviewers: bryce

Author: Pehrsons

mediacapture-record/MediaRecorder-events-and-exceptions.html

@@ -82,11 +82,11 @@
 
     assert_throws("NotSupportedError",
                   function() {
-                    recorder =
-                        new MediaRecorder(stream, {mimeType : "video/invalid"});
+                    recorder = new MediaRecorder(
+                      new MediaStream(), {mimeType : "video/invalid"});
                   },
                   "recorder should throw() with unsupported mimeType");
-    let recorder = new MediaRecorder(stream);
+    let recorder = new MediaRecorder(new MediaStream());
     assert_equals(recorder.state, "inactive");
 
     recorder.stop();
@@ -98,6 +98,14 @@
     assert_throws("InvalidStateError", function(){recorder.requestData()},
                   "cannot requestData() if recorder is in |inactive| state");
 
+    assert_throws("NotSupportedError",
+                  function() {
+                    recorder.start();
+                  },
+                  "recorder should throw() when starting with inactive stream");
+
+    recorder.stream.addTrack(stream.getTracks()[0]);
+
     drawSomethingOnCanvas();
 
     recorder.onstop = recorderOnUnexpectedEvent;