Use variadic template for screen handler's AddCallback.

Use variadic template for screen handler's AddCallback.

BUG=none

Committed: https://crrev.com/3d5f51b28af6131b5dec279f60a029af26fed037
Cr-Commit-Position: refs/heads/master@{#322444}

[xiyuan, 2015-03-26 18:29:42]

xiyuan@chromium.org changed reviewers:
+ dzhioev@chromium.org

[xiyuan, 2015-03-26 18:29:42]

Variadicc tempate for AddCallback in a separate CL. :) I am not expert of
templates so be careful with the change.

The only behavior change is we now CHECK() instead of NOTREACHED() for bad arg
in the passed ListValue. I like CHECK better because it catches problem in
release build. Also it is more straightforward and natural to use with variadic
parameter expansion.

[dzhioev (left Google), 2015-03-26 18:53:03]

On 2015/03/26 18:29:42, xiyuan wrote:
> Variadicc tempate for AddCallback in a separate CL. :) I am not expert of
> templates so be careful with the change.
> 
> The only behavior change is we now CHECK() instead of NOTREACHED() for bad arg
> in the passed ListValue. I like CHECK better because it catches problem in
> release build. Also it is more straightforward and natural to use with
variadic
> parameter expansion.

From my experience with templates -- if code compiles, it works =)
LGTM

[xiyuan, 2015-03-26 19:20:37]

The CQ bit was checked by xiyuan@chromium.org

[commit-bot: I haz the power, 2015-03-26 19:21:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1038003002/1

[commit-bot: I haz the power, 2015-03-26 19:24:12]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-26 19:24:49]

Patchset 1 (id:??) landed as
https://crrev.com/3d5f51b28af6131b5dec279f60a029af26fed037
Cr-Commit-Position: refs/heads/master@{#322444}