Mark '\f' as an ASCII whitespace character in IsAsciiWhitespace

The whatwg spec includes '\f' as an ASCII whitespace character:
https://infra.spec.whatwg.org/#ascii-whitespace

The lack of this character was causing failures in data URL parsing
tests.

Bug: 807562
Change-Id: I8f939cfb1cf1307a468734d8ae1e633f4206718f
Reviewed-on: https://chromium-review.googlesource.com/c/1472852
Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632248}
5 files changed