Make SkFontMgr interface const.

Make SkFontMgr interface const.

COLLABORATOR=mtklein@chromium.org
BUG=skia:

Committed: http://code.google.com/p/skia/source/detail?r=13314

[reed1, 2014-02-04 19:08:37]

Why does it have to be thread-safe? -- none of the calls that might trigger
init() are const.

Not sure why this was deferred, unless it is very expensive, and we sometimes
don't call it...?

[mtklein, 2014-02-04 19:54:07]

Have a look?  I'm being a little optimistic by editing here and trying on
trybots, so modulo, you know, being correct, how does this look?

[reed1, 2014-02-04 20:10:19]

appears that the only places we needed 'mutable' were real gosh darn caches, and
those have explicit mutex protection.

If so... lgtm

[mtklein_C, 2014-02-04 20:59:37]

On 2014/02/04 20:10:19, reed1 wrote:
> appears that the only places we needed 'mutable' were real gosh darn caches,
and
> those have explicit mutex protection.
> 
> If so... lgtm

Yup.  Feels good.

[bungeman-skia, 2014-02-04 21:09:34]

If it passes the bots, lgtm.

[mtklein, 2014-02-04 22:03:29]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-02-04 22:22:28]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/mtklein@google.com/134643028/90001

[commit-bot: I haz the power, 2014-02-04 22:35:05]

Change committed as 13314