Avoid heap allocation in SkPictureStateTree constructor

This makes empty state trees cheaper. ~1% improvement on rasterize_and_record_micro.key_silk_cases on Android.

BUG=1772
R=tomhudson@chromium.org, tomhudson@google.com

Author: skyostil@chromium.org

Review URL: https://codereview.chromium.org/111573002

git-svn-id: http://skia.googlecode.com/svn/trunk@12616 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed