Reland of Add experiment on weak ping delay during call set up time

Reland of Add experiment on weak ping delay during call set up time (patchset #1 id:1 of https://codereview.webrtc.org/1416773003/ )

Reason for revert:
https://codereview.chromium.org/1419253002 is landed to address this linker issue. Keep my fingers crossed.

Original issue's description:
> Revert of Add experiment on weak ping delay during call set up time (patchset #4 id:60001 of https://codereview.webrtc.org/1411883002/ )
>
> Reason for revert:
> This CL breaks Chromium, undefined reference link error to webrtc::field_trial::FindFullName. Adding the dependency system_wrappers to the rtc_p2p target is not enough to fix this.
>
> Looking at field_trial.h (in system_wrappers/interface/, not to be confused with the one in test/) the documentation says "WebRTC clients MUST provide an implementation of: ...FindFullName... Or link with a default one provided in: ...system_wrappers.gyp:field_trial_default).
>
> So maybe just depend on field_trial_default? Not sure what should be done in case there are implications to adding this dependency, I'm reverting this. Sorry :)
>
> Original issue's description:
> > Add experiment on weak ping delay during call set up time
> >
> > BUG=
> > R=pthatcher@webrtc.org
> >
> > Committed: https://crrev.com/3bf69b15f4c0c0ca4ab17c237084684a37bb8279
> > Cr-Commit-Position: refs/heads/master@{#10343}
>
> TBR=pthatcher@webrtc.org,juberti@webrtc.org,guoweis@webrtc.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=
>

TBR=pthatcher@webrtc.org,juberti@webrtc.org,hbos@webrtc.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Committed: https://crrev.com/b0bb77fd615c5ce413b16f6157b2ffc25898631f
Cr-Commit-Position: refs/heads/master@{#10418}

[guoweis_webrtc, 2015-10-26 22:09:45]

Created Reland of Add experiment on weak ping delay during call set up time

[commit-bot: I haz the power, 2015-10-26 22:09:56]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1413603005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1413603005/1

[commit-bot: I haz the power, 2015-10-26 22:10:05]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-26 22:10:17]

Patchset 1 (id:??) landed as
https://crrev.com/b0bb77fd615c5ce413b16f6157b2ffc25898631f
Cr-Commit-Position: refs/heads/master@{#10418}