Linux, Mac: Don't test parent directories when checking if a path is writable.
Linux, Mac: Don't test parent directories when checking if a path is writable.

This additional check has existed since the code was first written, but wtc
queried it in [1] and noted that it doesn't match the Windows version.

[1] http://codereview.chromium.org/541022/diff/1/3#newcode309

Removing this additional test doesn't break any unittests so it looks
like we can match the Windows code here.

http://codereview.chromium.org/545156

git-svn-id: http://src.chromium.org/svn/trunk/src@36760 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 154b4da1b6b779a8f27d8e48ca93268df4d37c7b
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser