Fix divide-by-zero in program cache tracking.

This also adds tracking to developer builds.

Author: jvanverth@google.com

Reviewed By: robertphillips@google.com

Review URL: https://chromiumcodereview.appspot.com/12426019

git-svn-id: http://skia.googlecode.com/svn/trunk@8284 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed