Oilpan: IDL union objects should be put in HeapVector

Source/bindings/tests/results/modules/UnionTypesModules.h

Index: Source/bindings/tests/results/modules/UnionTypesModules.h
diff --git a/Source/bindings/tests/results/modules/UnionTypesModules.h b/Source/bindings/tests/results/modules/UnionTypesModules.h
index ac0cbdf574a45a36deb25ee98b28641948e7d1ad..e13093b912c2f1757f2f4c5b079a1cba8c00ca00 100644
--- a/Source/bindings/tests/results/modules/UnionTypesModules.h
+++ b/Source/bindings/tests/results/modules/UnionTypesModules.h
@@ -75,4 +75,10 @@ struct NativeValueTraits<BooleanOrString> {
 
 } // namespace blink
 
+// We need to set canInitializeWithMemset=true because HeapVector supports
+// items that can initialize with memset or have a vtable. It is safe to
+// set canInitializeWithMemset=true for a union type object in practice.
+// See https://codereview.chromium.org/1118993002/#msg5 for more details.
+WTF_ALLOW_MOVE_AND_INIT_WITH_MEM_FUNCTIONS(blink::BooleanOrString);
+
 #endif // UnionTypeModules_h