946819 - Replace hardcoded _volumeStackMarginEnd value with the computed value after one of the preexisting synchronous reflows

Status: NEW

(Toolkit :: Video/Audio Controls, defect)

Description

[Jared Wein [:jaws] (please needinfo? me)]

From https://bugzilla.mozilla.org/show_bug.cgi?id=649490#c59:
In toolkit/content/widgets/videocontrols.xml:
> @@ +1376,5 @@
> > +                    let isAudioOnly = this.isAudioOnly;
> > +                    if (isAudioOnly) {
> > +                      // When the fullscreen button is hidden we add margin-end to the volume stack.
> > +                      let volumeStack = document.getAnonymousElementByAttribute(this.videocontrols, "class", "volumeStack");
> > +                      let volumeStackCS = doc.defaultView.getComputedStyle(volumeStack);

> Hohum. This will trigger a reflow. Can we avoid this, or hardcode the 
> value instead? A lot of other stuff is hardcoded here, so I'm not really 
> sure why we need to fetch this dynamically.

From https://bugzilla.mozilla.org/show_bug.cgi?id=649490#c61:
> This generally looks good. The 8px thing is kind of sad but it was also sad 
> the other way, and we do the same thing with e.g. the overlaid play button. 
> If you feel like it, let's file a followup to get that info dynamically 
> rather than hardcoding it.

> (Yes, I know I said to hardcode it; that's just because a reflow in that 
> place isn't great, but there's other code in the video controls that fetches 
> a bunch of clientWidths, we could probably bunch it up there with some >
> refactoring work, but I don't want to hold up this bug)