Add normal map sample

This adds an example of an SkShader that does normal
mapping. It has a single directional light and an
ambient light.

Committed: https://skia.googlesource.com/skia/+/8e0da72ba890de395c9946ec6639c9e1e7b16027

Review URL: https://codereview.chromium.org/1212813009
4 files changed