Remove SkShader virtual method validContext

src/effects/gradients/SkSweepGradient.cpp

Index: src/effects/gradients/SkSweepGradient.cpp
diff --git a/src/effects/gradients/SkSweepGradient.cpp b/src/effects/gradients/SkSweepGradient.cpp
index 0baf5c717eec9b6b30c1b5a5880f78fc388d41f6..81ebb3441eb13159399ce771d05c0a5e3402953d 100644
--- a/src/effects/gradients/SkSweepGradient.cpp
+++ b/src/effects/gradients/SkSweepGradient.cpp
@@ -56,11 +56,7 @@ size_t SkSweepGradient::contextSize() const {
     return sizeof(SweepGradientContext);
 }
 
-SkShader::Context* SkSweepGradient::createContext(const ContextRec& rec, void* storage) const {
-    if (!this->validContext(rec)) {
-        return NULL;
-    }
-
+SkShader::Context* SkSweepGradient::onCreateContext(const ContextRec& rec, void* storage) const {
     return SkNEW_PLACEMENT_ARGS(storage, SweepGradientContext, (*this, rec));
 }