[Mac] Fix use-after-free when dragging tabs with page-actions....

[Mac] Fix use-after-free when dragging tabs with page-actions.

This patches in the relevant bit of r38299:
    http://src.chromium.org/viewvc/chrome?view=rev&revision=38299 

> When dragging and dropping a tab who's window is going away entirely,
> the LocationBarViewMac instance and the PageActionViewList w/in go
> away before the cell.  Sometimes windows can re-display while being
> closed, then BANG.

BUG=34110
TEST=Install an extension which shows a page action (*).  Bring up two
tabs, drag one with the page action off to a separate window.  Drag it
back into the first window.

(*) For instance, the "Subscribe in Feed Reader" example at
http://code.google.com/chrome/extensions/samples.html , then browse to
Google News to get a page action.


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=38400

[Scott Hess - ex-Googler, 2010-02-08 20:52:55]

The original CL doesn't drover at all well due to conflicts, so this just
patches over the bit which fixes the actual bug.  I've build and tested against
307, and for good measure run valgrind over the indicated unit tests.

[Scott Hess - ex-Googler, 2010-02-08 21:00:01]

On 2010/02/08 20:52:55, shess wrote:
> The original CL doesn't drover at all well due to conflicts, so this just
> patches over the bit which fixes the actual bug.  I've build and tested
against
> 307, and for good measure run valgrind over the indicated unit tests.

BTW, looks like gcl submitted to trybots, which I'm going to guess will be full
of fail, since this is on the branch.

[Pam (message me for reviews), 2010-02-08 21:41:28]

LGTM.

- Pam