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

src/effects/gradients/SkTwoPointRadialGradient.cpp

Index: src/effects/gradients/SkTwoPointRadialGradient.cpp
diff --git a/src/effects/gradients/SkTwoPointRadialGradient.cpp b/src/effects/gradients/SkTwoPointRadialGradient.cpp
index 103e7d41c9ca445c52fbb2ab887bf698117fff36..03e1f0db84e86eeb2c046f47b78e79443a3e653c 100644
--- a/src/effects/gradients/SkTwoPointRadialGradient.cpp
+++ b/src/effects/gradients/SkTwoPointRadialGradient.cpp
@@ -220,6 +220,7 @@ SkShader::GradientType SkTwoPointRadialGradient::asAGradient(
     return kRadial2_GradientType;
 }
 
+#if 0
 void SkTwoPointRadialGradient::shadeSpan(int x, int y, SkPMColor* dstCParam,
                                          int count) {
     SkASSERT(count > 0);
@@ -306,6 +307,7 @@ bool SkTwoPointRadialGradient::setContext( const SkBitmap& device,
     fFlags &= ~kHasSpan16_Flag;
     return true;
 }
+#endif
 
 #ifdef SK_DEVELOPER
 void SkTwoPointRadialGradient::toString(SkString* str) const {