Revert of Remove default args to several PageWidgetDelegate members. (patchset #2 id:20001 of https://codereview.chromium.org/603883002/)

Reason for revert:
Broke several cross-site iframe tests.

Original issue's description:
> Remove default args to several PageWidgetDelegate members.
> 
> No one passes the correct local root here yet; eventually, something....
> 
> BUG=411993
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=182705

TBR=japhet@chromium.org,kenrb@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=411993

Review URL: https://codereview.chromium.org/600823005

git-svn-id: svn://svn.chromium.org/blink/trunk@182716 bbb929c8-8fbe-4397-9dbb-9b2b20218538