some utils for rect and matrix

src/core/SkRasterizer.cpp

Index: src/core/SkRasterizer.cpp
diff --git a/src/core/SkRasterizer.cpp b/src/core/SkRasterizer.cpp
index 3a7af955551fb66d3a7c33c05e22729721fc1e44..ab9e011761bf54ae608c972989805ca7deb2348c 100644
--- a/src/core/SkRasterizer.cpp
+++ b/src/core/SkRasterizer.cpp
@@ -27,8 +27,7 @@ bool SkRasterizer::rasterize(const SkPath& fillPath, const SkMatrix& matrix,
         if (!filter->filterMask(&dstM, srcM, matrix, &margin)) {
             return false;
         }
-        storage = *clipBounds;
-        storage.inset(-margin.fX, -margin.fY);
+        storage = clipBounds->makeOutset(margin.fX, margin.fY);
         clipBounds = &storage;
     }