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

Author: fmalita@chromium.org

Review URL: https://codereview.chromium.org/29143005

git-svn-id: http://skia.googlecode.com/svn/trunk/src@11862 2bbb7eff-a529-9590-31e7-b0007b416f81
5 files changed