R1:5784e3d3c0cf

Omit "type" attribute from "<source />" tags in "<video>" to trick Chrome into playing them

Summary:
Fixes T13135. See PHI633. For at least some video files with legitimate MIME type "video/quicktime", Chrome can play them but refuses to if the `<source />` tag has a `type="video/quicktime"` attribute.

To trick Chrome into giving these videos the old college try, omit the "type" attribute. Chrome then tries to play the video, seems to realize it can, and we're back on track.

Since the "type" attribute…