enforce 16byte alignment in shader contexts

src/effects/gradients/SkSweepGradient.h

Index: src/effects/gradients/SkSweepGradient.h
diff --git a/src/effects/gradients/SkSweepGradient.h b/src/effects/gradients/SkSweepGradient.h
index ec6df45c645c5afb9510d0af63c353fb2539bf06..f458cea8ce773a47eb2c8a4ff721f5bb7ddd0740 100644
--- a/src/effects/gradients/SkSweepGradient.h
+++ b/src/effects/gradients/SkSweepGradient.h
@@ -15,8 +15,6 @@ class SkSweepGradient : public SkGradientShaderBase {
 public:
     SkSweepGradient(SkScalar cx, SkScalar cy, const Descriptor&);
 
-    size_t contextSize(const ContextRec&) const override;
-
     class SweepGradientContext : public SkGradientShaderBase::GradientShaderBaseContext {
     public:
         SweepGradientContext(const SkSweepGradient& shader, const ContextRec&);
@@ -41,6 +39,7 @@ public:
 
 protected:
     void flatten(SkWriteBuffer& buffer) const override;
+    size_t onContextSize(const ContextRec&) const override;
     Context* onCreateContext(const ContextRec&, void* storage) const override;
 
 private: