Revert 157076 "Allow context-less document dispatching events."

Caused crashes of WebGL context lost conformance tests.

> Allow context-less document dispatching events.
> 
> This change allows context-less documents like ones from XHR to
> dispatch events. More precicely, it allows event listeners in these documents
> to react dispatched events.
> 
> For that purpose, it introduces Document::m_contextDocument
> which points the document of the context where the document is created.
> 
> To prevent inline event handlers on context-less documents from being fired,
> the change extracts the eligibility check from V8LazyEventLitener
> to Document::allowInlineEventHandlers() and tightens it, so that it says no
> if the owner document of the event-holding node doesn't have context (=Frame).
> 
> BUG=275285
> TEST=event-on-created-document.html, event-on-xhr-document.html, import-events.html,
>      sub-imports-onload.html
> R=abarth@chromium.org, dglazkov@chromium.org, esprehn@chromium.org
> 
> Review URL: https://chromiumcodereview.appspot.com/23330004

TBR=morrita@chromium.org
BUG=285357,275285

Review URL: https://codereview.chromium.org/23627006

git-svn-id: svn://svn.chromium.org/blink/trunk@157241 bbb929c8-8fbe-4397-9dbb-9b2b20218538