enforce 16byte alignment in shader contexts

src/core/SkBlitter.cpp

Index: src/core/SkBlitter.cpp
diff --git a/src/core/SkBlitter.cpp b/src/core/SkBlitter.cpp
index c7c903dc6bcff4e2a305c13911abb7bda8a1bc58..bb5cfb72e3af36efa20663c014f8d1f2e3b14499 100644
--- a/src/core/SkBlitter.cpp
+++ b/src/core/SkBlitter.cpp
@@ -592,7 +592,7 @@ public:
         SkSafeUnref(fProxy);
     }
 
-    size_t contextSize(const ContextRec& rec) const override {
+    size_t onContextSize(const ContextRec& rec) const override {
         size_t size = sizeof(Sk3DShaderContext);
         if (fProxy) {
             size += fProxy->contextSize(rec);