Fix grit to substitute GRIT_DIR properly on Windows.

Fix grit to substitute GRIT_DIR properly on Windows.

Previously GRIT_DIR was replaced with the current path only when it's
followed by forward slash. GYP msvs generator replaces forward slashes
with back slashes which breaks GRIT_DIR substitution. Fixed GRIT_DIR
processing code to handle the case when GRIT_DIR is followed by back
slash.

Committed: https://code.google.com/p/grit-i18n/source/detail?r=84

[Sergey Ulanov, 2012-11-02 20:49:42]

This should fix the issue I had when landing
http://codereview.chromium.org/11275101/ (see
http://build.chromium.org/p/chromium.win/builders/Win%20Builder/builds/2896/s...
)

[Jói, 2012-11-05 09:23:19]

LGTM