Increase default DevTools request timeout to 30 seconds.

Increase default DevTools request timeout to 30 seconds.

The timeout was recently changed from None (wait forever) to 5 seconds.
On slow bots, even after _WaitForBrowserToComeUp returns, the launch of
the first renderer can take considerable time. The next request for the
browser's state is subject to the timeout here, and the browser does not
respond until the renderer's launch completes.

Increasing the timeout to 30 seconds should not regress the original fix
and should fix the flakiness.

BUG=403981
TBR=tonyg@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=290133

[Ken Russell (switch to Gerrit), 2014-08-16 02:44:40]

Tony: I'm CQ'ing this TBR'd because the cause is well understood at this point
and has very little risk of regressing the previous fix. We need to eliminate
this cause of flakiness in order to continue diagnosing other issues on these
bots.

[Ken Russell (switch to Gerrit), 2014-08-16 02:44:43]

The CQ bit was checked by kbr@chromium.org

[commit-bot: I haz the power, 2014-08-16 02:45:35]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/kbr@chromium.org/474413002/1

[commit-bot: I haz the power, 2014-08-16 08:23:01]

Committed patchset #1 (1) as 290133