Remove leading '/' when creating SyncFileSystem URL

So that giving an absolute path doesn't result in a path like:
'filesystem://<origin>/external/syncfs//foo'

BUG=none
TEST=manual

Review URL: https://codereview.chromium.org/98463004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238087 0039d316-1c4b-4281-b951-d872f2087c98
cr tool] Don't visit disabled nodes

BUG=316397

Review URL: https://codereview.chromium.org/95613005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238088 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238087
SVN changes up to revision 238088