Revert of Revert of Fix use-after-free in WebSocketHost::AddChannel()

Revert of Revert of Fix use-after-free in WebSocketHost::AddChannel() (patchset #1 id:1 of https://codereview.chromium.org/1006293002/)

Reason for revert:
The breakage still persists https://crbug.com/467471 after the original CL was reverted.

Original issue's description:
> Revert of Fix use-after-free in WebSocketHost::AddChannel() (patchset #3 id:40001 of https://codereview.chromium.org/998173003/)
>
> Reason for revert:
> Speculatively revert for https://crbug.com/467471
>
> Original issue's description:
> > Fix heap-use-after-free in WebSocketHost::AddChannel()
> >
> > WebSocketHost can be deleted in channel_->SendAddChannelRequest() and this
> > caused heap-use-after-free when |pending_flow_control_quota_| is accessed in
> > WebSocketHost::AddChannel().
> > This CL fixes it by posting OnFlowControl() with WeakPtr instead of calling
> > SendFlowControl() directly in WebSocketHost::AddChannel().
> >
> > BUG=466335
> >
> > Committed: https://crrev.com/d3a1d188162e45f75c87a218a70681c5d92139a8
> > Cr-Commit-Position: refs/heads/master@{#320260}
>
> TBR=ricea@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=466335
>
> Committed: https://crrev.com/4f078b9b59cbf2c1ea7098835c6488fa32d46474
> Cr-Commit-Position: refs/heads/master@{#320703}

TBR=ricea@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=466335
Committed: https://crrev.com/222d9a4c90248be97823499f2b2636e4abcf5422
Cr-Commit-Position: refs/heads/master@{#320716}

[hiroshige, 2015-03-16 12:56:46]

Created Revert of Revert of Fix use-after-free in WebSocketHost::AddChannel()

[commit-bot: I haz the power, 2015-03-16 12:57:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1014543002/1

[commit-bot: I haz the power, 2015-03-16 12:57:29]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-16 12:57:55]

Patchset 1 (id:??) landed as
https://crrev.com/222d9a4c90248be97823499f2b2636e4abcf5422
Cr-Commit-Position: refs/heads/master@{#320716}