Pepper: Add unit test for FileSystemResource.

Adds a unit test for file system resources.
Test Open failure cases.
Test RequestQuota.

BUG=194304

Review URL: https://codereview.chromium.org/113773006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242888 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242888