Add test to exercise extreme blur sigmas

src/effects/SkBlurMask.cpp

Index: src/effects/SkBlurMask.cpp
===================================================================
--- src/effects/SkBlurMask.cpp	(revision 11085)
+++ src/effects/SkBlurMask.cpp	(working copy)
@@ -873,7 +873,7 @@
 
     float variance = sigma * sigma;
 

[robertphillips, 2013/09/05 13:30:38]

The 4x window still had some edge effects (when compared to the brute force 1D
convolution).

-    int windowSize = SkScalarCeil(sigma*4);
+    int windowSize = SkScalarCeil(sigma*6);
     // round window size up to nearest odd number
     windowSize |= 1;
 
@@ -885,7 +885,7 @@
 
     float windowSum = 1;
     for (int x = 1 ; x <= halfWindow ; ++x) {
-        float gaussian = expf(-x*x / variance);
+        float gaussian = expf(-x*x / (2*variance));

[humper, 2013/09/05 14:19:23]

WHOOPS, nice catch.

         gaussWindow[halfWindow + x] = gaussWindow[halfWindow-x] = gaussian;
         windowSum += 2*gaussian;
     }