[DevTools] Force page redraw when enabling screencast.

[DevTools] Force page redraw when enabling screencast.

When attaching to a static page, it may not produce new frames, thus
rendering screencast useless. Forcing a frame helps in this case.

BUG=none

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=287421

[dgozman, 2014-08-04 08:35:15]

Could you please take a look?

Pavel - at content/browser/devtools;
Jochen - at content/;
Tom - at view_messages.

Thanks,
Dmitry

[pfeldman, 2014-08-04 09:07:01]

lgtm

[jochen (gone - plz use gerrit), 2014-08-04 09:09:58]

lgtm

[Tom Sepez, 2014-08-04 17:05:51]

Messages LGTM.

[dgozman, 2014-08-04 17:25:46]

The CQ bit was checked by dgozman@chromium.org

[commit-bot: I haz the power, 2014-08-04 17:27:09]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/dgozman@chromium.org/441623004/1

[commit-bot: I haz the power, 2014-08-04 19:16:45]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_chromium_chromeos_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[commit-bot: I haz the power, 2014-08-05 00:48:05]

Change committed as 287421