Add public Chromecast histograms.

Add public Chromecast histograms.

Also removes some outdated histograms that weren't supposed to be in the
public histogram list.  See bug 18595525.

BUG=20493841
Committed: https://crrev.com/89d63e4b8e8718ed969ee556281bd79a19817051
Cr-Commit-Position: refs/heads/master@{#329501}

[Bryan Eyler, 2015-05-11 22:57:40]

bryaneyler@google.com changed reviewers:
+ asvitkine@chromium.org, rkaplow@chromium.org

[rkaplow, 2015-05-12 14:54:31]

lgtm

[Alexei Svitkine (slow), 2015-05-12 15:12:23]

lgtm, assuming all the ones being removed are / will be added to the internal
file

[Bryan Eyler, 2015-05-12 17:46:44]

On 2015/05/12 15:12:23, Alexei Svitkine wrote:
> lgtm, assuming all the ones being removed are / will be added to the internal
> file

Platform.Temperature.Junction, Platform.DiskUsageData, and
Platform.DiskUsageCache are all in the internal one already.  Network.Wifi
removals are related to bug 18595525, but I could leave them in if there's a
concern about that cleanup.

[Bryan Eyler, 2015-05-12 19:42:01]

The CQ bit was checked by bryaneyler@google.com

[commit-bot: I haz the power, 2015-05-12 19:43:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1131673008/1

[commit-bot: I haz the power, 2015-05-12 21:49:59]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-12 21:51:11]

Patchset 1 (id:??) landed as
https://crrev.com/89d63e4b8e8718ed969ee556281bd79a19817051
Cr-Commit-Position: refs/heads/master@{#329501}