Trying to add the same scaled image twice shouldn't assert.

This unbreaks bench_pictures --multi foo for me.

BUG=skia:1868
R=reed@google.com

Author: mtklein@google.com

Review URL: https://codereview.chromium.org/89293002

git-svn-id: http://skia.googlecode.com/svn/trunk@12422 2bbb7eff-a529-9590-31e7-b0007b416f81
3 files changed