Change default value of video to true for getDisplayMedia calls

This CL makes sure the default value of video MediaStreamConstraints is false when called by getUserMedia() and true when called by
getDisplayMedia() and getDisplayMediaSet().

Spec: https://www.w3.org/TR/screen-capture/#ref-for-dom-displaymediastreamoptions-video-1

Bug: 904831
Change-Id: I28d7f3c7ffb7078108881c99361a6f4849f31081
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3945509
Commit-Queue: Fr <beaufort.francois@gmail.com>
Reviewed-by: Elad Alon <eladalon@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1058592}

screen-capture/getdisplaymedia.https.html

@@ -59,7 +59,6 @@
  {video: true},
  {video: true, audio: false},
  {audio: false},
- {audio: true},
  {},
  undefined
 ].forEach(constraints => promise_test(async t => {
@@ -93,6 +92,7 @@
 
 [
  {video: true, audio: true},
+ {audio: true},
 ].forEach(constraints => promise_test(async t => {
   const stream = await getDisplayMedia(constraints);
   t.add_cleanup(() => stopTracks(stream));