Fix the regex flatting html to prevent misdetection

Fix the regex flatting html to prevent misdetection

In some case, the previous regex may mistake to detect a wrong part as a
script/link tag. This patch fixes it.

Landing for yoshiki@chromium.org, original patch at https://codereview.chromium.org/11953014/

Committed: https://code.google.com/p/grit-i18n/source/detail?r=104

[Jói, 2013-01-22 12:36:25]

Yoshiki, this is my patch-in of your patch.  Will land it TBR.  You will need to
close the original code review manually by pressing the X icon next to the issue
number at http://codereview.chromium.org/.

Cheers,
Jói