Bug 1534991 - Make the pictureinpicture.svg reference Nightly-only for now in videocontrols.css. r=jaws

Differential Revision: https://phabricator.services.mozilla.com/D23406

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

toolkit/themes/shared/media/videocontrols.css

@@ -424,6 +424,7 @@
   background-image: url(chrome://global/skin/media/error.png);
 }
 
+%ifdef NIGHTLY_BUILD
 .statusIcon[type="pictureInPicture"] {
   min-width: 84px;
   min-height: 84px;
@@ -432,6 +433,7 @@
   fill: #fff;
   stroke: #fff;
 }
+%endif
 
 /* Overlay Play button */
 .clickToPlay {