Helper classes to scope undo action.

Helper classes to scope undo action.

Added 2 helper classes that allow scoping of the suspension of undo
tracking and grouping actions for undo.

BUG=126092
R=sky

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=214459

[Tom Cassiotis, 2013-07-26 18:48:27]

sky@ please take a look.

I took your cue to reduce the size of the CL. This change is self contained and
did not need to be part of https://codereview.chromium.org/19287013/

[sky, 2013-07-26 19:26:43]

thanks, LGTM

[commit-bot: I haz the power, 2013-07-26 20:54:19]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tom.cassiotis@gmail.com/20571004/1

[commit-bot: I haz the power, 2013-07-26 21:44:08]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tom.cassiotis@gmail.com/20571004/1

[commit-bot: I haz the power, 2013-07-27 23:51:01]

Retried try job too often on win7_aura for step(s) interactive_ui_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win7_aura&...

[commit-bot: I haz the power, 2013-07-29 15:45:30]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tom.cassiotis@gmail.com/20571004/1

[commit-bot: I haz the power, 2013-07-30 03:17:54]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tom.cassiotis@gmail.com/20571004/1

[commit-bot: I haz the power, 2013-07-30 14:41:42]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tom.cassiotis@gmail.com/20571004/1

[commit-bot: I haz the power, 2013-07-30 23:02:08]

Change committed as 214459