Use WeakPtr for RTCPeerConnectionHandler and RTCPeerConnectionTracker.

Use WeakPtr for RTCPeerConnectionHandler and RTCPeerConnectionTracker.
These objects don't have the same lifetime and we were using raw pointers to them  in a few places, which could lead to use-after-free.

BUG=429477
TBR=perkj@chromium.org
NOTRY=true

Committed: https://crrev.com/2c0f13b39d6ff1a867385e1acb7e6793a0440519
Cr-Commit-Position: refs/heads/master@{#302398}

[tommi (sloooow) - chröme, 2014-11-02 08:49:05]

The CQ bit was checked by tommi@chromium.org

[commit-bot: I haz the power, 2014-11-02 08:49:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/698803002/1

[tommi (sloooow) - chröme, 2014-11-02 10:04:45]

The CQ bit was unchecked by tommi@chromium.org

[tommi (sloooow) - chröme, 2014-11-02 10:04:59]

The CQ bit was checked by tommi@chromium.org

[tommi (sloooow) - chröme, 2014-11-02 10:05:26]

The CQ bit was unchecked by tommi@chromium.org

[tommi (sloooow) - chröme, 2014-11-02 10:06:06]

The CQ bit was checked by tommi@chromium.org

[tommi (sloooow) - chröme, 2014-11-02 10:07:01]

The CQ bit was unchecked by tommi@chromium.org

[tommi (sloooow) - chröme, 2014-11-02 10:11:32]

The CQ bit was checked by tommi@chromium.org

[commit-bot: I haz the power, 2014-11-02 10:12:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/698803002/1

[commit-bot: I haz the power, 2014-11-02 10:12:25]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-11-02 10:13:04]

Patchset 1 (id:??) landed as
https://crrev.com/2c0f13b39d6ff1a867385e1acb7e6793a0440519
Cr-Commit-Position: refs/heads/master@{#302398}