HTMLParser should use current value of scriptEnabled flag

This CL adds caching  of scriptEnabled setting to Document.

When page is reloaded we create new parser throught DocumentLoader::ensureWriter
and set scriptEnabled flag. ContentSettingsObserver::allowScript method is
responsible for checking settings but it uses cache. Cache is cleared on
DidCommitProvisionalLoad but parser is already created before that. However we
can't clear cache earlier because unload events for old page might be fired and
it depends on old page settings (cached).

BUG=232410

Review URL: https://codereview.chromium.org/313173012

git-svn-id: svn://svn.chromium.org/blink/trunk@177664 bbb929c8-8fbe-4397-9dbb-9b2b20218538