Bug 1565374 - Improve test. r=jib

Differential Revision: https://phabricator.services.mozilla.com/D37783

--HG--
extra : moz-landing-system : lando

dom/media/tests/mochitest/test_fingerprinting_resistance.html

@@ -22,7 +22,11 @@ async function testEnumerateDevices(expectDevices) {
 
 async function testGetUserMedia(expectDevices) {
   const constraints = [
-    {audio: true}, {video: true}, {audio: true, video: true}
+    {audio: true},
+    {video: true},
+    {audio: true, video: true},
+    {video: {width: {min: 1e9}}}, // impossible
+    {audio: {channelCount: {exact: 1e3}}}, // impossible
   ];
   for (let constraint of constraints) {
     let message = "getUserMedia(" + JSON.stringify(constraint) + ")";