Refactoring the tests in http/tests/security/javascriptURL

1. They should work outside TestRunner now that they rely only on
   postMessage, and not the ugly 'testRunner.globalFlag' hack.

2. One JS file controls all the execution context changes, which
   will make future changes simpler.

Review URL: https://codereview.chromium.org/27181003

git-svn-id: svn://svn.chromium.org/blink/trunk@159648 bbb929c8-8fbe-4397-9dbb-9b2b20218538