Cleanup: Add fileapi::GetIsolatedFileSystemRootURIString

to hide the details how we create a root URI string for IsolatedFileSystems
from each extension code.

BUG=none
TEST=existing tests

Review URL: https://codereview.chromium.org/11833002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@176036 0039d316-1c4b-4281-b951-d872f2087c98
4 files changed