Revert "binding: Window-returning attributes return null if a Window is detached."

This reverts commit eb73fb7bd81b3253a36171851da62e15e5f88b41.

The root cause of https://crbug.com/621730 was not related to the binding layer,
and https://crrev.com/2085983002 caused regressions as reported at
https://crbug.com/629840 , so let's revert the CL.

BUG=629840,621730

Review-Url: https://codereview.chromium.org/2177383004
Cr-Commit-Position: refs/heads/master@{#407750}
2 files changed