Harden degenerate gradient context handling

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 d99d979f6899d9f6812f8f141a3f1088b2352450..d1fe269b9cb228e29f0dc46aba1e619bec3a6415 100644
--- a/src/effects/gradients/SkSweepGradient.cpp
+++ b/src/effects/gradients/SkSweepGradient.cpp
@@ -50,7 +50,7 @@ size_t SkSweepGradient::onContextSize(const ContextRec&) const {
 }
 
 SkShader::Context* SkSweepGradient::onCreateContext(const ContextRec& rec, void* storage) const {
-    return new (storage) SweepGradientContext(*this, rec);
+    return CheckedCreateContext<SweepGradientContext>(storage, *this, rec);
 }
 
 SkSweepGradient::SweepGradientContext::SweepGradientContext(