Activate scrollbars (etc.) upon selecting a tab....

Activate scrollbars (etc.) upon selecting a tab.

(Conceivably, the SetActive() could be pushed into the RWHV's
DidBecomeSelected(). Conceivably, one could imagine selection without
activation, so I chose to put it closer to the UI side of the code in
the TabContents. Hmmm. Maybe we should also put in the RWHV::SetActive()
method on all platforms.)

BUG=18262
TEST=Make your browser window really small, create new tabs, switch between them.

[Avi (use Gerrit), 2009-08-04 14:48:15]

LG; should you set SetActive(false) on switching out the tab?

[viettrungluu-gmail, 2009-08-04 17:50:52]

On 2009/08/04 14:48:15, Avi wrote:
> LG; should you set SetActive(false) on switching out the tab?

That's a good question. Philosophically, maybe. On the other hand, the
de-selected tab won't be displayed, so there's no particular reason to change
it. (I worried for a moment that it might not work correctly when ripping out a
tab, but I guess the old window loses key status, so it does get updated
correctly.)

[Avi (use Gerrit), 2009-08-04 19:06:05]

Cool. Well, go for the commit then.

[Avi (use Gerrit), 2009-08-04 21:59:56]

On 2009/08/04 19:06:05, Avi wrote:
> Cool. Well, go for the commit then.

Committed r22422.