Revert of Revert of DevTools: do not mute the protocol channel while reattaching.

Revert of Revert of DevTools: do not mute the protocol channel while reattaching. (patchset #1 id:1 of https://codereview.chromium.org/958573002/)

Reason for revert:
DevToolsSanityTest.TestReattachAfterCrash doesn't check anything now, and this patch wasn't an origin of the flakiness on OSX 10.6. DevToolsSanityTest.TestReattachAfterCrash was disabled, so I reland original patch.


Original issue's description:
> Revert of DevTools: do not mute the protocol channel while reattaching. (patchset #1 id:1 of https://codereview.chromium.org/945303002/)
> 
> Reason for revert:
> DevToolsSanityTest.TestReattachAfterCrash is flaky on OSX 10.6 after this patch
> 
> Original issue's description:
> > DevTools: do not mute the protocol channel while reattaching.
> > Otherwise sync notifications are not going through.
> > 
> > BUG=460697
> > 
> > Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=190745
> 
> TBR=dgozman@chromium.org,yurys@chromium.org,pfeldman@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=460697, 461616
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=190817

TBR=dgozman@chromium.org,yurys@chromium.org,pfeldman@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=460697, 461616
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=190832

[sergeyv, 2015-02-25 14:49:12]

Created Revert of Revert of DevTools: do not mute the protocol channel while
reattaching.

[commit-bot: I haz the power, 2015-02-25 14:50:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/959723002/1

[yurys, 2015-02-25 14:50:45]

lgtm

[commit-bot: I haz the power, 2015-02-25 14:50:49]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=190832