Harden degenerate gradient context handling

src/effects/gradients/SkLinearGradient.cpp

Index: src/effects/gradients/SkLinearGradient.cpp
diff --git a/src/effects/gradients/SkLinearGradient.cpp b/src/effects/gradients/SkLinearGradient.cpp
index be29540add6abf78c9469af23e996b3f396f18d7..a249ae4ac82c2195ce2e559978cf057ce0a8377a 100644
--- a/src/effects/gradients/SkLinearGradient.cpp
+++ b/src/effects/gradients/SkLinearGradient.cpp
@@ -82,8 +82,8 @@ size_t SkLinearGradient::onContextSize(const ContextRec& rec) const {
 
 SkShader::Context* SkLinearGradient::onCreateContext(const ContextRec& rec, void* storage) const {
     return use_4f_context(rec, fGradFlags)
-        ? static_cast<SkShader::Context*>(new (storage) LinearGradient4fContext(*this, rec))
-        : static_cast<SkShader::Context*>(new (storage) LinearGradientContext(*this, rec));
+        ? CheckedCreateContext<LinearGradient4fContext>(storage, *this, rec)
+        : CheckedCreateContext<  LinearGradientContext>(storage, *this, rec);
 }
 
 // This swizzles SkColor into the same component order as SkPMColor, but does not actually