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

src/effects/gradients/SkRadialGradient.h

Index: src/effects/gradients/SkRadialGradient.h
diff --git a/src/effects/gradients/SkRadialGradient.h b/src/effects/gradients/SkRadialGradient.h
index 4ff3951b907f7f7c712c8aec37c0b1f9b21295e5..c8cae701914aef4cabe492a0cf9f6cdc9944c83e 100644
--- a/src/effects/gradients/SkRadialGradient.h
+++ b/src/effects/gradients/SkRadialGradient.h
@@ -14,10 +14,12 @@
 class SkRadialGradient : public SkGradientShaderBase {
 public:
     SkRadialGradient(const SkPoint& center, SkScalar radius, const Descriptor&);
+#if 0
     virtual void shadeSpan(int x, int y, SkPMColor* dstC, int count)
         SK_OVERRIDE;
     virtual void shadeSpan16(int x, int y, uint16_t* dstCParam,
                              int count) SK_OVERRIDE;
+#endif
     virtual BitmapType asABitmap(SkBitmap* bitmap,
                                  SkMatrix* matrix,
                                  TileMode* xy) const SK_OVERRIDE;