First pass at Rect Effect

include/core/SkMatrix.h

Index: include/core/SkMatrix.h
===================================================================
--- include/core/SkMatrix.h	(revision 8570)
+++ include/core/SkMatrix.h	(working copy)
@@ -90,6 +90,12 @@
      */
     bool isSimilarity(SkScalar tol = SK_ScalarNearlyZero) const;
 
+    /** Returns true if the matrix contains only translation, rotation or scale
+        (non-uniform scale is allowed).
+        Returns false if other transformation types are included or is degenerate
+     */
+    bool preservesRightAngles(SkScalar tol = SK_ScalarNearlyZero) const;
+
     enum {
         kMScaleX,
         kMSkewX,