Add ownership-transfer to histogram management calls.

Add ownership-transfer to histogram management calls.

Both histogram-persistence and statistics-recorder manage
ownership of histograms.  This CL changes the interface
to use scoped_ptr to explicitly document, with std::move,
when the transfer of ownership is taking place.

BUG=

Done as part of https://codereview.chromium.org/1738063002/

[bcwhite, 2016-02-10 22:42:45]

bcwhite@chromium.org changed reviewers:
+ asvitkine@chromium.org, grt@chromium.org

[bcwhite, 2016-02-10 22:42:46]

Note:  The changes to StaisticsRecorder are a bit complex.  I can back those out
and just update the GetPersistentHistogram() calls in histogram_persistence if
so desired.

[grt (UTC plus 2), 2016-02-11 15:02:16]

I'll leave it to you, Alexei. In general, I'm a fan of making ownership transfer
explicit by use of scoped_ptr, so I like the direction.

[bcwhite, 2016-02-27 19:28:47]

On 2016/02/11 15:02:16, grt wrote:
> I'll leave it to you, Alexei. In general, I'm a fan of making ownership
transfer
> explicit by use of scoped_ptr, so I like the direction.

Histogram changes now part of https://codereview.chromium.org/1738063002/

Statistics recorder part could still be done if so desired after other CL is
submitted and this one rebased.

[bcwhite, 2016-03-16 02:51:00]

Description was changed from

==========
Add ownership-transfer to histogram management calls.

Both histogram-persistence and statistics-recorder manage
ownership of histograms.  This CL changes the interface
to use scoped_ptr to explicitly document, with std::move,
when the transfer of ownership is taking place.

BUG=
==========

to

==========
Add ownership-transfer to histogram management calls.

Both histogram-persistence and statistics-recorder manage
ownership of histograms.  This CL changes the interface
to use scoped_ptr to explicitly document, with std::move,
when the transfer of ownership is taking place.

BUG=
==========

[bcwhite, 2016-03-16 02:51:34]

Description was changed from

==========
Add ownership-transfer to histogram management calls.

Both histogram-persistence and statistics-recorder manage
ownership of histograms.  This CL changes the interface
to use scoped_ptr to explicitly document, with std::move,
when the transfer of ownership is taking place.

BUG=
==========

to

==========
Add ownership-transfer to histogram management calls.

Both histogram-persistence and statistics-recorder manage
ownership of histograms.  This CL changes the interface
to use scoped_ptr to explicitly document, with std::move,
when the transfer of ownership is taking place.

BUG=

Done as part of https://codereview.chromium.org/1738063002/
==========