Add TabManager class, relocate Tab to common/.

Add TabManager class, relocate Tab to common/.
(Piecemeal review-only CL - won't be submitted or compiled as-is;
instead, it will be merged into a larger CL which will also go out for
review at a later date.)

R=wez@chromium.org
BUG=

[Kevin M, 2016-09-29 18:02:12]

Description was changed from

==========
Add TabManager class, relocate Tab to common/.
(Piecemeal review-only CL - won't be submitted or compiled as-is;
instead, it will be merged into a larger CL which will also go out for
review at a later date.)

R=wez@chromium.org
BUG=
==========

to

==========
Add TabManager class, relocate Tab to common/.
(Piecemeal review-only CL - won't be submitted or compiled as-is;
instead, it will be merged into a larger CL which will also go out for
review at a later date.)

R=wez@chromium.org
BUG=
==========

[Kevin M, 2016-09-29 18:02:12]

Description was changed from

==========
Add TabManager class, relocate Tab to common/.
(Piecemeal review-only CL - won't be submitted or compiled as-is;
instead, it will be merged into a larger CL which will also go out for
review at a later date.)

R=wez@chromium.org
BUG=
==========

to

==========
Add TabManager class, relocate Tab to common/.
(Piecemeal review-only CL - won't be submitted or compiled as-is;
instead, it will be merged into a larger CL which will also go out for
review at a later date.)

R=wez@chromium.org
BUG=
==========