Bug 1585769 - Create a fresh <video> element for the Picture-in-Picture player window rather than cloning the original element. r=JSON_voorhees

Cloning the original node was needed when we needed the MediaInfo copied over, but
HTMLVideoElement::CloneElementVisually copies it over for us, so we can create a
fresh <video> element. This should also be a much healthier thing to do
security-wise, since we're not cloning strange nodes from the web.

Differential Revision: https://phabricator.services.mozilla.com/D48123

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

toolkit/actors/PictureInPictureChild.jsm

@@ -947,21 +947,8 @@ class PictureInPictureChild extends ActorChild {
     }
 
     let doc = this.content.document;
-    // Clone the original video to get its MediaInfo (specifically, it's dimensions)
-    // set right away, but also pause the video since we don't need two copies of it
-    // playing at the same time. The originating video will be "projected" onto the
-    // cloned Picture-in-Picture player video via cloneElementVisually.
-    let playerVideo = originatingVideo.cloneNode();
-    playerVideo.pause();
-    playerVideo.removeAttribute("controls");
+    let playerVideo = doc.createElement("video");
 
-    // Mute the video and rely on the originating video's audio playback.
-    // This way, we sidestep the AutoplayPolicy blocking stuff.
-    playerVideo.muted = true;
-
-    // Strip any inline styles off of the video, and try to get rid of any surrounding
-    // whitespace.
-    playerVideo.setAttribute("style", "");
     doc.body.style.overflow = "hidden";
     doc.body.style.margin = "0";