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>
diff --git a/samplecode/SampleShadowUtils.cpp b/samplecode/SampleShadowUtils.cpp
index 858d212..f5b6635 100755
--- a/samplecode/SampleShadowUtils.cpp
+++ b/samplecode/SampleShadowUtils.cpp
@@ -105,7 +105,7 @@
     }
 
     void drawBG(SkCanvas* canvas) {
-        canvas->drawColor(0xFFDDDDDD);
+        canvas->drawColor(0xFFFFFFFF);
     }
 
     void drawShadowedPath(SkCanvas* canvas, const SkPath& path,