Added Z scale when X and Y scale to spot lights and point lights

Z scale is set as the average of X scale and Y scale.

BUG=skia:
R=senorblanco@google.com, senorblanco@chromium.org

Author: sugoi@chromium.org

Review URL: https://codereview.chromium.org/198013002

git-svn-id: http://skia.googlecode.com/svn/trunk@13798 2bbb7eff-a529-9590-31e7-b0007b416f81
3 files changed