XSSAuditor: treat questionmark as a non-canonical character.

We've seen recent examples of servers that replace an invalid set of
of high-bytes with a literal questionmark.  We are already excluding
the high bytes from consideration, so we do the same with the
questionmark to ensure a match should this happen.

To test this, we hack up our "server script" to replace an arbitrary high
byte with a questionmark. This is sufficient for testing although it may
not match any real server.

BUG=395351

Review URL: https://codereview.chromium.org/421623003

git-svn-id: svn://svn.chromium.org/blink/trunk@179161 bbb929c8-8fbe-4397-9dbb-9b2b20218538