Push API: Remove AddAppHandlerIfNecessary to prevent DCHECK

Push API: Remove AddAppHandlerIfNecessary to prevent DCHECK

Previously we would try to add the app handler twice for the first
registration - once in AddAppHandlerIfNecessary called by RegisterFrom*,
then again in IncreasePushRegistrationCount called by RegisterEnd.

Adding the app handler a second time causes GCMDriver to DCHECK.

It's ok to just add it in IncreasePushRegistrationCount (it was never
actually necessary to have a GCMAppHandler to register).

BUG=436453
Committed: https://crrev.com/d20f0147a03e5485ea95d25123dd8050fd2d0e2b
Cr-Commit-Position: refs/heads/master@{#310523}

[johnme, 2015-01-08 14:21:51]

johnme@chromium.org changed reviewers:
+ mvanouwerkerk@chromium.org

[Michael van Ouwerkerk, 2015-01-08 16:08:06]

lgtm

[johnme, 2015-01-08 16:28:13]

The CQ bit was checked by johnme@chromium.org

[commit-bot: I haz the power, 2015-01-08 16:28:45]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/823993003/1

[commit-bot: I haz the power, 2015-01-08 17:27:21]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-08 17:28:15]

Patchset 1 (id:??) landed as
https://crrev.com/d20f0147a03e5485ea95d25123dd8050fd2d0e2b
Cr-Commit-Position: refs/heads/master@{#310523}