Refactor resize filter to go faster

src/core/SkBitmapFilter.cpp

Index: src/core/SkBitmapFilter.cpp
diff --git a/src/core/SkBitmapFilter.cpp b/src/core/SkBitmapFilter.cpp
index 55a7092ba7840b303375bc0dc86ea8f07fdb74d2..d96a3854050c78456049a32d61070f5784cebe6c 100644
--- a/src/core/SkBitmapFilter.cpp
+++ b/src/core/SkBitmapFilter.cpp
@@ -20,7 +20,7 @@ SK_CONF_DECLARE(const char *, c_bitmapFilter, "bitmap.filter", "mitchell", "Whic
 
 SkBitmapFilter *SkBitmapFilter::Allocate() {
     if (!strcmp(c_bitmapFilter, "mitchell")) {
-        return new SkMitchellFilter(1.f / 3.f, 1.f / 3.f);
+        return new SkMitchellFilter;
     } else if (!strcmp(c_bitmapFilter, "lanczos")) {
         return new SkLanczosFilter;
     } else if (!strcmp(c_bitmapFilter, "hamming")) {