Push sigma-based blur interface into our GMs/benches/tests/samplecode

gm/megalooper.cpp

Index: gm/megalooper.cpp
===================================================================
--- gm/megalooper.cpp	(revision 11004)
+++ gm/megalooper.cpp	(working copy)
@@ -110,10 +110,10 @@
     }
 
     SkMaskFilter* createBlur() {
-        static const SkScalar kBlurRadius = 25.0f;
+        static const SkScalar kBlurSigma = SkFloatToScalar(14.93375f);
 
-        return SkBlurMaskFilter::Create(kBlurRadius,
-                                        SkBlurMaskFilter::kNormal_BlurStyle,
+        return SkBlurMaskFilter::Create(SkBlurMaskFilter::kNormal_BlurStyle,
+                                        kBlurSigma,
                                         SkBlurMaskFilter::kHighQuality_BlurFlag);
     }