Files.app: Fix a CSS path in a JavaScript file.

CSS directory is moved from css to foreground/css.
This CL fix a CSS path in a JavaScript file.

BUG=none
TEST=manually
TBR=yoshiki@chromium.org

Review URL: https://codereview.chromium.org/55683003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232671 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232671