Make ChannelMojoHost::ChannelDelegate a RefContedThreadSafe

Make ChannelMojoHost::ChannelDelegate a RefContedThreadSafe

ChannelDelegate::GetWeakPtr() was called from the UI thread but
it was racy as the weak ptr is also used in the IO thread.
This CL turns ChannelDelegate a ThreadSafeRefCounted so that
we can pass ChannelDelegate itself to the task runner, instead
of using its weak ptr on the UI thread.

This change also turns some TaskRunner declarations to
SequencedTaskRunner to access its DeleteSoon() API from
ChannelDelegate.

TBR=creis@chromium.org
R=viettrungluu@chrormium.org, agl@chromium.org
BUG=460243
Committed: https://crrev.com/70b91498930876d016b9716f2cc267373287976d
Cr-Commit-Position: refs/heads/master@{#318994}

[agl, 2015-02-25 00:24:24]

RS LGTM for ipc/

[Hajime Morrita, 2015-02-25 19:07:55]

Trung: Ping?

[Hajime Morrita, 2015-03-02 21:26:36]

OK, it's all green now.
Trung, could you take a look? This is a TSAN detected race fix.

[Hajime Morrita, 2015-03-03 20:18:22]

Trung: Ping?

[Hajime Morrita, 2015-03-03 23:08:23]

The CQ bit was checked by morrita@chromium.org

[Hajime Morrita, 2015-03-03 23:08:23]

The patchset sent to the CQ was uploaded after l-g-t-m from agl@chromium.org
Link to the patchset: https://codereview.chromium.org/955813002/#ps20001 (title:
"Updated to ToT")

[commit-bot: I haz the power, 2015-03-03 23:10:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/955813002/20001

[commit-bot: I haz the power, 2015-03-03 23:44:06]

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

[commit-bot: I haz the power, 2015-03-03 23:44:08]

Try jobs failed on following builders:
  android_chromium_gn_compile_rel on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/android_chromiu...)

[Hajime Morrita, 2015-03-04 00:04:43]

The CQ bit was checked by morrita@chromium.org

[Hajime Morrita, 2015-03-04 00:04:46]

The patchset sent to the CQ was uploaded after l-g-t-m from agl@chromium.org
Link to the patchset: https://codereview.chromium.org/955813002/#ps40001 (title:
"Landing")

[commit-bot: I haz the power, 2015-03-04 00:05:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/955813002/40001

[commit-bot: I haz the power, 2015-03-04 01:52:46]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-03-04 01:53:40]

Patchset 3 (id:??) landed as
https://crrev.com/70b91498930876d016b9716f2cc267373287976d
Cr-Commit-Position: refs/heads/master@{#318994}