enforce 16byte alignment in shader contexts

src/core/SkEmptyShader.h

Index: src/core/SkEmptyShader.h
diff --git a/src/core/SkEmptyShader.h b/src/core/SkEmptyShader.h
index c1713d1a2ee91e7a4bbabcaed144589911d4c204..42b61c52feffa9478817fe9edd212eb5a281d2da 100644
--- a/src/core/SkEmptyShader.h
+++ b/src/core/SkEmptyShader.h
@@ -20,16 +20,16 @@ class SK_API SkEmptyShader : public SkShader {
 public:
     SkEmptyShader() {}
 
-    size_t contextSize(const ContextRec&) const override {
-        // Even though createContext returns nullptr we have to return a value of at least
-        // sizeof(SkShader::Context) to satisfy SkSmallAllocator.
-        return sizeof(SkShader::Context);
-    }
-
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkEmptyShader)
 
 protected:
+    size_t onContextSize(const ContextRec&) const override {
+        // Even though createContext returns nullptr we have to return a value of at least
+        // sizeof(SkShader::Context) to satisfy SkSmallAllocator.
+        return SkAlign16(sizeof(SkShader::Context));
+    }
+
     SkShader::Context* onCreateContext(const ContextRec&, void*) const override {
         return nullptr;
     }