Add support for WeakPtr<T>

Add support for WeakPtr<T>
The implementation is borrowed from Chromium.

Also change use of raw pointers in VideoSendStreamImpl to use WeakPtr<>

BUG=webrtc:6289
Committed: https://crrev.com/8ff860a35d611a976d94a18cb0778bf96b704427
Cr-Commit-Position: refs/heads/master@{#14468}

[perkj_webrtc, 2016-09-23 14:47:54]

perkj@webrtc.org changed reviewers:
+ tommi@webrtc.org

[perkj_webrtc, 2016-09-23 14:47:55]

Something like this.

[perkj_webrtc, 2016-09-30 11:56:24]

On 2016/09/23 14:47:55, perkj_webrtc wrote:
> Something like this.

ptal

[tommi, 2016-09-30 12:05:59]

lgtm!

[perkj_webrtc, 2016-09-30 12:10:24]

The CQ bit was checked by perkj@webrtc.org

[commit-bot: I haz the power, 2016-09-30 12:10:29]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.webrtc.org/...

[commit-bot: I haz the power, 2016-09-30 14:11:02]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-09-30 14:11:03]

Try jobs failed on following builders:
  android_arm64_rel on master.tryserver.webrtc (JOB_TIMED_OUT, no build URL)

[perkj_webrtc, 2016-10-03 05:35:12]

The CQ bit was checked by perkj@webrtc.org

[commit-bot: I haz the power, 2016-10-03 05:35:15]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.webrtc.org/...

[commit-bot: I haz the power, 2016-10-03 06:42:58]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-10-03 06:42:58]

Try jobs failed on following builders:
  linux_rel on master.tryserver.webrtc (JOB_FAILED,
http://build.chromium.org/p/tryserver.webrtc/builders/linux_rel/builds/18864)

[perkj_webrtc, 2016-10-03 07:04:22]

The CQ bit was checked by perkj@webrtc.org

[commit-bot: I haz the power, 2016-10-03 07:04:26]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.webrtc.org/...

[commit-bot: I haz the power, 2016-10-03 07:30:08]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2016-10-03 07:30:12]

Description was changed from

==========
Add support for WeakPtr<T>
The implementation is borrowed from Chromium.

Also change use of raw pointers in VideoSendStreamImpl to use WeakPtr<>

BUG= webrtc:6289
==========

to

==========
Add support for WeakPtr<T>
The implementation is borrowed from Chromium.

Also change use of raw pointers in VideoSendStreamImpl to use WeakPtr<>

BUG= webrtc:6289

Committed: https://crrev.com/8ff860a35d611a976d94a18cb0778bf96b704427
Cr-Commit-Position: refs/heads/master@{#14468}
==========

[commit-bot: I haz the power, 2016-10-03 07:30:13]

Patchset 4 (id:??) landed as
https://crrev.com/8ff860a35d611a976d94a18cb0778bf96b704427
Cr-Commit-Position: refs/heads/master@{#14468}