View Page Source don't work for SVG files

[Sh1d0w]

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).

Fixes #4054

Auditors:
@bbondy

Test Plan:
1.Open an svg link Eg: https://w3c.github.io/svgwg/specs/svg-authoring/examples/clock-animate-1.svg
2.Right click to open the context menu
3.Click "View page source"

[bbondy]

people might actually want to view the svg source because it is a vector non binary xml format. Do other browsers not allow you to do this?

[bbondy]

oh sorry I read that reversed, you are removing svg from the list, so I agree :)