Make numTextures() be non-virtual on GrCustomStage.

R=tomhudson@google.com,robertphillips@google.com,senorblanco@chromium.org
Review URL: https://codereview.appspot.com/6586081

git-svn-id: http://skia.googlecode.com/svn/trunk@5805 2bbb7eff-a529-9590-31e7-b0007b416f81
8 files changed