Use fast path for circular shadows.

Also cleans up some of the MaskFilter code to make it
more correct.

BUG=skia:6119

Change-Id: I93016bcdd9c55fcb2d1dc8776428a72eb563d67a
Reviewed-on: https://skia-review.googlesource.com/9116
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/samplecode/SampleAndroidShadows.cpp b/samplecode/SampleAndroidShadows.cpp
index 803ea49..cad8f50 100644
--- a/samplecode/SampleAndroidShadows.cpp
+++ b/samplecode/SampleAndroidShadows.cpp
@@ -469,7 +469,7 @@
         canvas->translate(-250, 110);
         lightPos.fX -= 250;
         lightPos.fY += 110;
-        this->drawShadowedPath(canvas, fCirclePath, SkTMax(1.0f, 8+fZDelta), paint, 0,
+        this->drawShadowedPath(canvas, fCirclePath, SkTMax(1.0f, 8+fZDelta), paint, kAmbientAlpha,
                                lightPos, kLightWidth, 0.5f);
 
         paint.setColor(SK_ColorGREEN);