Bug 1397793 - Don't use the AEC on a 440Hz tone when testing that audio is flowing. r=pehrsons

This brings in a lot of noise and makes the test fail.

MozReview-Commit-ID: 70EGM1q1J24

--HG--
extra : rebase_source : f19c191747f2e63303406a43a79454e4ea1ed428
extra : histedit_source : f27d34204de924ab30b5718b240ac3d23677991c

dom/media/tests/mochitest/test_getUserMedia_mediaElementCapture_audio.html

@@ -16,7 +16,7 @@ createHTML({
 var audioContext;
 var gUMAudioElement;
 var analyser;
-runTest(() => getUserMedia({audio: true})
+runTest(() => getUserMedia({audio: { echoCancellation: false }})
   .then(stream => {
     gUMAudioElement = createMediaElement("audio", "gUMAudio");
     gUMAudioElement.srcObject = stream;