Fix window.history GC issue. Since the history object is not part of...

Fix window.history GC issue.  Since the history object is not part of
the DOM, we need to explicitly keep the history wrapper object alive
for the lifetime of the DOMWindow object with which it is associated.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=12543

[Mads Ager (chromium), 2009-03-26 12:17:48]

First batch of GC changes.  More objects need this treatment, but in order to do
that, I need to land a WebKit change first.

[Søren Thygesen Gjesse, 2009-03-26 12:29:26]

LGTM

Do we have a GC test for this, or was the test fixed by this just flaky before?

[Mads Ager (chromium), 2009-03-26 12:32:32]

The test fixed by this failed consistently on Windows and not on Mac and Linux. 
When I do the full change, I will add a GC layout test for all the objects.