Add unit tests for NetworkDelegate::CanAccessFile

This was requested during https://codereview.chromium.org/38303002/.

R=mmenke@chromium.org

Review URL: https://codereview.chromium.org/50393004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234297 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234297