enforce 16byte alignment in shader contexts

src/effects/gradients/SkSweepGradient.cpp

Index: src/effects/gradients/SkSweepGradient.cpp
diff --git a/src/effects/gradients/SkSweepGradient.cpp b/src/effects/gradients/SkSweepGradient.cpp
index de80c79ae046236dabc7a8df996a6793c8319991..12d55e8b49118abcca3882a5b26b7405a118a7e6 100644
--- a/src/effects/gradients/SkSweepGradient.cpp
+++ b/src/effects/gradients/SkSweepGradient.cpp
@@ -45,8 +45,8 @@ void SkSweepGradient::flatten(SkWriteBuffer& buffer) const {
     buffer.writePoint(fCenter);
 }
 
-size_t SkSweepGradient::contextSize(const ContextRec&) const {
-    return sizeof(SweepGradientContext);
+size_t SkSweepGradient::onContextSize(const ContextRec&) const {
+    return SkAlign16(sizeof(SweepGradientContext));
 }
 
 SkShader::Context* SkSweepGradient::onCreateContext(const ContextRec& rec, void* storage) const {