Remove SkShader virtual method validContext

src/effects/gradients/SkLinearGradient.cpp

Index: src/effects/gradients/SkLinearGradient.cpp
diff --git a/src/effects/gradients/SkLinearGradient.cpp b/src/effects/gradients/SkLinearGradient.cpp
index b9de651fcecac83bc6876cd03d5bbe1a2ac5cd80..f37759c1a94ff416b8ce8b0e19444409fcd7e861 100644
--- a/src/effects/gradients/SkLinearGradient.cpp
+++ b/src/effects/gradients/SkLinearGradient.cpp
@@ -76,11 +76,7 @@ size_t SkLinearGradient::contextSize() const {
     return sizeof(LinearGradientContext);
 }
 
-SkShader::Context* SkLinearGradient::createContext(const ContextRec& rec, void* storage) const {
-    if (!this->validContext(rec)) {
-        return NULL;
-    }
-
+SkShader::Context* SkLinearGradient::onCreateContext(const ContextRec& rec, void* storage) const {
     return SkNEW_PLACEMENT_ARGS(storage, LinearGradientContext, (*this, rec));
 }