FileAPI: Clean up ObfuscatedFileUtil::GetDirectoryDatabase signature

This is a preparation patch for the issue (see BUG line).

ObfuscatedFileUtil::GetDirectoryDatabase should accept not a pair of OriginURL
and FileSystemType but FileSystemURL so that it'll be able to treat an
irregular filesystem (i.e. isolated-sandboxed filesystem).


BUG=286240
TEST=content_unittests --gtest_filter=ObfuscatedFileUtilTest.*
NOTRY=true

Review URL: https://codereview.chromium.org/26223004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228130 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228130