I first need to figure out what to do about window.document before we
can deprecate this: window.document is a regular accessor, however, once
the window navigated from about:blank, its value will never change.
Blink uses ForceSet to then replace the accessor with a data constant
which has way better performance than invoking the accessor all the
time.

Since the accessor, however, is installed as read only &
non-configurable, there is no spec compliant way to pull this off right
now

BUG=chromium:595601
R=verwaest@chromium.org
LOG=y

Review URL: https://codereview.chromium.org/1816033002

Cr-Commit-Position: refs/heads/master@{#34919}