We use img tag for showing the loading spinner in message edit form
and dialog-widget submit button, instead of object tag because using
object tag gives the following error- "Refused to display
'https://chat.zulip.org/' in a frame because it set 'X-Frame-Options'
to 'deny'." in the browser console.
As mentioned by Anders in czo, this is probably because we’re loading
the SVG using an <object> tag as if it’s totally-not-an-IE3-ActiveX-
control.
We also need to add a new svg file similar to loader.svg with the
change that the retangles are filled with black color. This needs
to be done because we cannot get access to the svg document if we
use img tag and so we cannot change the color of rectangles using
jquery as we were doing before to show the spinner depending on
day/night mode. So, now we just set the src attribute of img tag
to the correct svg file depending on day/night mode.
Discussed in #issues > loading tail-spin.svg denied by X-Frame-Options.
sahil839