Extract most of the mutable state of SkShader into a separate Context object.

src/effects/gradients/SkTwoPointRadialGradient.h

Index: src/effects/gradients/SkTwoPointRadialGradient.h
diff --git a/src/effects/gradients/SkTwoPointRadialGradient.h b/src/effects/gradients/SkTwoPointRadialGradient.h
index e050804b4654b00fb1166fa9f72fce5b177ab6c8..a0eb8f95ae747fdad923104d55d38b09365f2e41 100644
--- a/src/effects/gradients/SkTwoPointRadialGradient.h
+++ b/src/effects/gradients/SkTwoPointRadialGradient.h
@@ -23,11 +23,24 @@ public:
     virtual GradientType asAGradient(GradientInfo* info) const SK_OVERRIDE;
     virtual GrEffectRef* asNewEffect(GrContext* context, const SkPaint&) const SK_OVERRIDE;
 
-    virtual void shadeSpan(int x, int y, SkPMColor* dstCParam,
-                           int count) SK_OVERRIDE;
-    virtual bool setContext(const SkBitmap& device,
-                            const SkPaint& paint,
-                            const SkMatrix& matrix) SK_OVERRIDE;
+
+    virtual size_t contextSize() const SK_OVERRIDE;
+    bool validContext(const SkBitmap&, const SkPaint&, const SkMatrix&) const SK_OVERRIDE;
+    virtual SkShader::Context* createContext(const SkBitmap&, const SkPaint&, const SkMatrix&,
+                                             void* storage) const SK_OVERRIDE;
+
+    class TwoPointRadialGradientContext : public SkGradientShaderBase::GradientShaderBaseContext {
+    public:
+        TwoPointRadialGradientContext(const SkTwoPointRadialGradient& shader,
+                                      const SkBitmap& device,
+                                      const SkPaint& paint,
+                                      const SkMatrix& matrix);
+        ~TwoPointRadialGradientContext() {}
+
+        virtual void shadeSpan(int x, int y, SkPMColor dstC[], int count) SK_OVERRIDE;
+
+        typedef SkGradientShaderBase::GradientShaderBaseContext INHERITED;
+    };
 
     SkScalar getCenterX1() const { return fDiff.length(); }
     SkScalar getStartRadius() const { return fStartRadius; }