Reland of: [Presentation API] Implement ondefaultsessionstart in PSImpl.

Reland of: [Presentation API] Implement ondefaultsessionstart in PSImpl.

To fix PresentationServiceImplTest.DefaultSessionStartReset timeout
in  Android Tests (dbg).

TEST=git cl try + linux_android_dbg_ng
----

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/2ed5f820be60cfe8ef53f2e25605ae94bda8de0a
Cr-Commit-Position: refs/heads/master@{#326859}

[imcheng (use chromium acct), 2015-04-23 17:47:11]

imcheng@google.com changed reviewers:
+ avayvod@chromium.org, mfoltz@chromium.org

[imcheng (use chromium acct), 2015-04-23 17:47:19]

Patchset #2 (id:20001) has been deleted

[imcheng (use chromium acct), 2015-04-23 17:47:24]

Patchset #2 (id:40001) has been deleted

[mark a. foltz, 2015-04-23 18:10:02]

lgtm

[imcheng (use chromium acct), 2015-04-23 18:12:43]

The CQ bit was checked by imcheng@google.com

[commit-bot: I haz the power, 2015-04-23 18:14:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1055053004/60001

[imcheng (use chromium acct), 2015-04-23 18:31:55]

imcheng@google.com changed reviewers:
+ avi@chromium.org

[imcheng (use chromium acct), 2015-04-23 18:31:56]

+Avi for content/public/browser/presentation_service_delegate.h

[commit-bot: I haz the power, 2015-04-23 18:53:27]

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

[commit-bot: I haz the power, 2015-04-23 18:53:28]

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

[imcheng, 2015-04-24 18:22:25]

imcheng@chromium.org changed reviewers:
+ imcheng@chromium.org

[imcheng, 2015-04-24 18:22:25]

Ping for Avi.

[Avi (use Gerrit), 2015-04-24 18:40:50]

lgtm

[imcheng, 2015-04-24 18:41:18]

The CQ bit was checked by imcheng@chromium.org

[commit-bot: I haz the power, 2015-04-24 18:42:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1055053004/60001

[commit-bot: I haz the power, 2015-04-24 19:41:27]

Committed patchset #2 (id:60001)

[commit-bot: I haz the power, 2015-04-24 19:42:20]

Patchset 2 (id:??) landed as
https://crrev.com/2ed5f820be60cfe8ef53f2e25605ae94bda8de0a
Cr-Commit-Position: refs/heads/master@{#326859}