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

src/effects/gradients/SkRadialGradient.cpp

Index: src/effects/gradients/SkRadialGradient.cpp
diff --git a/src/effects/gradients/SkRadialGradient.cpp b/src/effects/gradients/SkRadialGradient.cpp
index efa82f49bf3aa3c2a8c8d93f83eb9eb185a1f243..dcbb7a7fe9b8927ff499e4eccc975956b2bf3d39 100644
--- a/src/effects/gradients/SkRadialGradient.cpp
+++ b/src/effects/gradients/SkRadialGradient.cpp
@@ -157,6 +157,7 @@ SkRadialGradient::SkRadialGradient(const SkPoint& center, SkScalar radius,
     rad_to_unit_matrix(center, radius, &fPtsToUnit);
 }
 
+#if 0
 void SkRadialGradient::shadeSpan16(int x, int y, uint16_t* dstCParam,
                          int count) {
     SkASSERT(count > 0);
@@ -212,6 +213,7 @@ void SkRadialGradient::shadeSpan16(int x, int y, uint16_t* dstCParam,
         } while (--count != 0);
     }
 }
+#endif
 
 SkShader::BitmapType SkRadialGradient::asABitmap(SkBitmap* bitmap,
     SkMatrix* matrix, SkShader::TileMode* xy) const {
@@ -389,6 +391,7 @@ void shadeSpan_radial_repeat(SkScalar fx, SkScalar dx, SkScalar fy, SkScalar dy,
 
 }  // namespace
 
+#if 0
 void SkRadialGradient::shadeSpan(int x, int y,
                                 SkPMColor* SK_RESTRICT dstC, int count) {
     SkASSERT(count > 0);
@@ -436,6 +439,7 @@ void SkRadialGradient::shadeSpan(int x, int y,
         } while (--count != 0);
     }
 }
+#endif
 
 /////////////////////////////////////////////////////////////////////