When clicking on the media timeline, compute the percentage along the
timeline's width the user clicked, and set the playback time to the same
percentage of the video's duration.
When the control bar is shown, do not toggle playback when clicking on
the control bar, unless the click target is the playback button. This
will let us implement clicking on the timeline to seek.
Note that this requires caching some layout rects on the video element.
We need to remember where the corresponding layout boxes are, and we
can't cache them on the layout box, as that may be destroyed any time.
The layout node, and therefore the painting box, is frequently destroyed
and recreated. This causes us to forget the cached mouse position we use
to highlight media controls. Move this cached position to the DOM node
instead, which survives relayout.
The link color is what closely resembled the color I was going for on
the machine I originally developed the controls on. But turns out this
is a very dark blue on most Serenity themes. Instead, hard-code the
original intended color, which is a lighter blue.
Rather than storing static DevicePixels dimensions, treat the desired
pixel sizes as CSSPixels and convert them to DevicePixels.
This was originally developed on a mac with a device-to-CSS-pixel ratio
of 2. Running it on another machine with a ratio of 1 made the controls
appear huge.
If the video element has a 'controls' attribute, we now paint some basic
video controls over the video element. If no frame has been decoded yet,
we paint a play button on the center of the element.
If a frame has been decoded, we paint that frame and paint a control bar
on the bottom of the frame. This control bar currently only contains a
play/pause button, depending on the video's playback state. We will only
paint the control bar if the video is paused or hovered.
