More analytic shadow refactoring.

This is mostly to simplify and reduce redundant calculations.

Change-Id: I895bd43fbc9defd812969870c2145f9f19d69a6b
Reviewed-on: https://skia-review.googlesource.com/15462
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
8 files changed