Hopefully detect/prevent crash in PageInfoBubbleView::OnWidgetDestroying()

Make sure that the callback is not null, and that we use the widget that
is reported being closed rather than calling GetWidget() - just in case
the view has somehow come unglued from the widget.

I really can't think of any other way this could crash.

Bug: 966308
Change-Id: Ic0c2ee9adb8b1e26326c1300238db058e5022819
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1627817
Commit-Queue: Dana Fried <dfried@chromium.org>
Commit-Queue: Bret Sepulveda <bsep@chromium.org>
Auto-Submit: Dana Fried <dfried@chromium.org>
Reviewed-by: Bret Sepulveda <bsep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662826}
1 file changed