Constify SkFlattenable::getFactory().

Constify SkFlattenable::getFactory().

This allows us to also constify the argument of
SkFlattenableWriteBuffer::writeFlattenable() - which I've recently found
myself const-casting for no apparent good reason.

R=reed@google.com,mtklein@google.com,bungeman@google.com

Committed: http://code.google.com/p/skia/source/detail?r=11862

[reed1, 2013-10-18 19:24:19]

lgtm

[mtklein, 2013-10-18 19:28:44]

On 2013/10/18 19:24:19, reed1 wrote:
> lgtm

This has always puzzled me.  Major +1.  lgtm

[commit-bot: I haz the power, 2013-10-18 19:37:39]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/fmalita@chromium.org/29143005/1

[commit-bot: I haz the power, 2013-10-18 19:37:59]

Change committed as 11862

[robertphillips, 2013-10-20 13:43:20]

Reverted in r11871 due to Chromium compilation failures. Please see:

https://codereview.chromium.org/30973002/

[f(malita), 2013-10-21 04:16:11]

On 2013/10/20 13:43:20, robertphillips wrote:
> Reverted in r11871 due to Chromium compilation failures. Please see:
> 
> https://codereview.chromium.org/30973002/

Rolling this into Chromium requires updating the getFactory() signature for a
couple of SkFlattenable-derived classes:
https://codereview.chromium.org/31613002

[robertphillips, 2013-10-21 12:26:52]

Relanded in r11876