enforce 16byte alignment in shader contexts

src/core/SkPictureShader.cpp

Index: src/core/SkPictureShader.cpp
diff --git a/src/core/SkPictureShader.cpp b/src/core/SkPictureShader.cpp
index f1addadd20012745373b76ce91b3bf3bcab98e99..630b1bf8e14c49227a731a38fafba767fb3e876a 100644
--- a/src/core/SkPictureShader.cpp
+++ b/src/core/SkPictureShader.cpp
@@ -241,8 +241,8 @@ SkShader* SkPictureShader::refBitmapShader(const SkMatrix& viewMatrix, const SkM
     return tileShader.detach();
 }
 
-size_t SkPictureShader::contextSize(const ContextRec&) const {
-    return sizeof(PictureShaderContext);
+size_t SkPictureShader::onContextSize(const ContextRec&) const {
+    return SkAlign16(sizeof(PictureShaderContext));
 }
 
 SkShader::Context* SkPictureShader::onCreateContext(const ContextRec& rec, void* storage) const {