Make DOMRequestState a thin wrapper of NewScriptState

This CL is a preparation to completely replace DOMRequestState with NewScriptState. For that goal, this CL makes DOMRequestState just a thin wrapper of NewScriptState as the first step.

BUG=357144

Review URL: https://codereview.chromium.org/227433003

git-svn-id: svn://svn.chromium.org/blink/trunk@170962 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: Report a creation of execution context in WorkerRuntimeAgent

BUG=

Review URL: https://codereview.chromium.org/227233002

git-svn-id: svn://svn.chromium.org/blink/trunk@170963 bbb929c8-8fbe-4397-9dbb-9b2b20218538