Improve HTMLProgressElement exception messages.

This is the third file I've edited that threw exceptions on Infinity
or NaN. I've extracted those messages out into an ExceptionMessages
helper, and adjusted the existing tests accordingly (there was a typo
in VTTRegion's message that this CL fixes)

BUG=270033

Review URL: https://codereview.chromium.org/83363002

git-svn-id: svn://svn.chromium.org/blink/trunk@162542 bbb929c8-8fbe-4397-9dbb-9b2b20218538