Converted CRWSessionController to use NavigationItems.

Converted CRWSessionController to use NavigationItems.

This CL introduces scoped and unscoped NavigationItemLists, and are
used to store the NavigationItems within CRWSessionController.
CRWSessionEntries no longer own their corresponding NavigationItems,
and are stored in a map managed by CRWSessionController.  The
CRWSessionEntry properties have been updated to return NavigationItems,
and the CRWSessionController selector names have been updated to refer
to NavigationItems rather than CRWSessionEntries.

BUG=454984

[kkhorimoto, 2017-02-02 23:13:20]

kkhorimoto@chromium.org changed reviewers:
+ eugenebut@chromium.org

[Eugene But (OOO till 7-30), 2017-02-02 23:25:10]

This is quite large CL which has safe parts (renaming) and unsaafe parts
(changing the implementation). Could you please split it into parts. Safe part
first and then one or more unsafe parts to follow up. 

Thanks!

[kkhorimoto, 2017-02-04 00:04:28]

Description was changed from

==========
Converted CRWSessionController to use NavigationItems.

This CL introduces scoped and unscoped NavigationItemLists, and are
used to store the NavigationItems within CRWSessionController.
CRWSessionEntries no longer own their corresponding NavigationItems,
and are stored in a map managed by CRWSessionController.  The
CRWSessionEntry properties have been updated to return NavigationItems,
and the CRWSessionController selector names have been updated to refer
to NavigationItems rather than CRWSessionEntries.

BUG=454984
==========

to

==========
Converted CRWSessionController to use NavigationItems.

This CL introduces scoped and unscoped NavigationItemLists, and are
used to store the NavigationItems within CRWSessionController.
CRWSessionEntries no longer own their corresponding NavigationItems,
and are stored in a map managed by CRWSessionController.  The
CRWSessionEntry properties have been updated to return NavigationItems,
and the CRWSessionController selector names have been updated to refer
to NavigationItems rather than CRWSessionEntries.

BUG=454984
==========

[kkhorimoto, 2017-02-04 00:05:11]

This CL was split into two smaller ones:

Interface name changes are here:
https://codereview.chromium.org/2671773005/

Logic changes are here:
https://codereview.chromium.org/2672953005/