Remove SkShader virtual method validContext

patch from issue 267923005

BUG=skia:
R=scroggo@google.com

Author: reed@google.com

Review URL: https://codereview.chromium.org/261773005

git-svn-id: http://skia.googlecode.com/svn/trunk@14573 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/effects/SkPerlinNoiseShader.cpp b/src/effects/SkPerlinNoiseShader.cpp
index a4944fb..c6d6118 100644
--- a/src/effects/SkPerlinNoiseShader.cpp
+++ b/src/effects/SkPerlinNoiseShader.cpp
@@ -425,11 +425,8 @@
     return SkPreMultiplyARGB(rgba[3], rgba[0], rgba[1], rgba[2]);
 }
 
-SkShader::Context* SkPerlinNoiseShader::createContext(const ContextRec& rec, void* storage) const {
-    if (!this->validContext(rec)) {
-        return NULL;
-    }
-
+SkShader::Context* SkPerlinNoiseShader::onCreateContext(const ContextRec& rec,
+                                                        void* storage) const {
     return SkNEW_PLACEMENT_ARGS(storage, PerlinNoiseShaderContext, (*this, rec));
 }