Randomize seed for SkDiscretePathEffect::filterPath()

include/effects/SkDiscretePathEffect.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkDiscretePathEffect_DEFINED
 #define SkDiscretePathEffect_DEFINED
 
 #include "SkPathEffect.h"
 
 /** \class SkDiscretePathEffect
 
     This path effect chops a path into discrete segments, and randomly displaces them.
 */
 class SK_API SkDiscretePathEffect : public SkPathEffect {
 public:
     /** Break the path into segments of segLength length, and randomly move the endpoints
         away from the original path by a maximum of deviation.
         Note: works on filled or framed paths
+
+        @param seedAssist This is a caller-supplied seedAssist that modifies
+                          the seed value that is used to randomize the path
+                          segments' endpoints. If not supplied it defaults to 0,
+                          in which case filtering a path multiple times will
+                          result in the same set of segments (this is useful for
+                          testing). If a caller does not want this behaviour
+                          they can pass in a different seedAssist to get a
+                          different set of path segments.
     */
-    static SkDiscretePathEffect* Create(SkScalar segLength, SkScalar deviation) {
-        return SkNEW_ARGS(SkDiscretePathEffect, (segLength, deviation));
+    static SkDiscretePathEffect* Create(SkScalar segLength,
+                                        SkScalar deviation,
+                                        uint32_t seedAssist=0) {
+        return SkNEW_ARGS(SkDiscretePathEffect,
+                          (segLength, deviation, seedAssist));
     }
 
     virtual bool filterPath(SkPath* dst, const SkPath& src,
                             SkStrokeRec*, const SkRect*) const SK_OVERRIDE;
 
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkDiscretePathEffect)
 
 protected:
-    SkDiscretePathEffect(SkScalar segLength, SkScalar deviation);
+    SkDiscretePathEffect(SkScalar segLength,
+                         SkScalar deviation,
+                         uint32_t seedAssist);
     explicit SkDiscretePathEffect(SkReadBuffer&);
     virtual void flatten(SkWriteBuffer&) const SK_OVERRIDE;
 
 private:
     SkScalar fSegLength, fPerterb;
 
+    /* Caller-supplied 32 bit seed assist */
+    uint32_t fSeedAssist;
+
     typedef SkPathEffect INHERITED;
 };
 
 #endif