Fast path for blurred round rects -- blur a small 9patch rect on the CPU

src/effects/SkBlurMask.h

Index: src/effects/SkBlurMask.h
diff --git a/src/effects/SkBlurMask.h b/src/effects/SkBlurMask.h
index f5c9f1d05078b4a822bafca6fe53e8c99782f569..39adb96f9a077970895ae6176ecc4e7202e0e50a 100644
--- a/src/effects/SkBlurMask.h
+++ b/src/effects/SkBlurMask.h
@@ -23,9 +23,16 @@ public:
                          SkIPoint *margin = NULL,
                          SkMask::CreateMode createMode =
                                                 SkMask::kComputeBoundsAndRenderImage_CreateMode);
+
+    // forceQuality will prevent BoxBlur from falling back to the low quality approach when sigma
+    // is very small -- this can be used predict the margin bump ahead of time without completely
+    // replicating the internal logic.  This permits not only simpler caching of blurred results,
+    // but also being able to predict precisely at what pixels the blurred profile of e.g. a
+    // rectangle will lie.
+
     static bool BoxBlur(SkMask* dst, const SkMask& src,
                         SkScalar sigma, SkBlurStyle style, SkBlurQuality quality,
-                        SkIPoint* margin = NULL);
+                        SkIPoint* margin = NULL, bool force_quality=false);
 
     // the "ground truth" blur does a gaussian convolution; it's slow
     // but useful for comparison purposes.