Refactor ModuleSystem so it passes an Isolate around

BUG=324225
R=marja@chromium.org

Review URL: https://codereview.chromium.org/98623003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238079 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238079