Revert of [Presentation API] Implement ondefaultsessionstart in PSImpl.

Revert of [Presentation API] Implement ondefaultsessionstart in PSImpl. (patchset #7 id:180001 of https://codereview.chromium.org/1073893003/)

Reason for revert:
Speculative revert to fix content_unittests failures: http://build.chromium.org/p/chromium.linux/builders/Android%20Tests%20%28dbg%29/builds/27420

Original issue's description:
> [Presentation API] Implement ondefaultsessionstart in PSImpl.
>
> Added DefaultSessionStartContext for coordinating sending default
> session back to PresentationDispatcher.
>
> When ListenForDefaultSessionStart is called, DefaultSessionStartContext
> will be installed on PresentationServiceImpl. When both the default
> session and PresentationDispatcher's callback are available, the
> callback will be invoked with the session.
>
> On Reset(), if a callback is available, it will be invoked with null.
> Changed PresentationDispatcher to not update Blink in that case.
>
> Also, PSImpl now keeps track of the corresponding RFH's ID instead of
> RFH* since most of the time we only need to use the ID.
>
> Changed PresentationServiceDelegate's Add/RemoveObserver interface,
> since the PresentationServiceDelegate need to be able to correlate
> an Observer with a RFH. (at most 1 per RFH, as it stands today).
>
> Added OnDefaultPresentationStarted to
> PresentationServiceDelegate::Observer interface and implemented it
> in PresentationServiceImpl.
>
> Added tests in PresentationServiceImpl.
>
> BUG=459001
>
> Committed: https://crrev.com/79ddfb2383dca537e481eb9e0a477267dd48bc60
> Cr-Commit-Position: refs/heads/master@{#326353}

TBR=avayvod@google.com,avi@chromium.org,imcheng@chromium.org,mfoltz@chromium.org,avayvod@chromium.org,imcheng@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=459001
Committed: https://crrev.com/89a5c0d4bc4e43ac69ee4db6a01916f41ccf2c0f
Cr-Commit-Position: refs/heads/master@{#326378}

[vmpstr, 2015-04-22 22:08:36]

Created Revert of [Presentation API] Implement ondefaultsessionstart in PSImpl.

[vmpstr, 2015-04-22 22:09:07]

The CQ bit was checked by vmpstr@chromium.org

[imcheng, 2015-04-22 22:10:38]

lgtm

[commit-bot: I haz the power, 2015-04-22 22:12:35]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1102683002/1

[commit-bot: I haz the power, 2015-04-22 22:16:11]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-22 22:17:04]

Patchset 1 (id:??) landed as
https://crrev.com/89a5c0d4bc4e43ac69ee4db6a01916f41ccf2c0f
Cr-Commit-Position: refs/heads/master@{#326378}