Bug 1727227: Add a static assert to ensure that the size of the AccAttributes value variant isn't unintentionally changed. r=eeejay

Differential Revision: https://phabricator.services.mozilla.com/D123415

accessible/base/AccAttributes.h

@@ -40,6 +40,7 @@ class AccAttributes {
 
   using AttrValueType =
       Variant<bool, float, int32_t, RefPtr<nsAtom>, CSSCoord, FontSize, Color>;
+  static_assert(sizeof(AttrValueType) <= 16);
   using AtomVariantMap = nsTHashMap<nsRefPtrHashKey<nsAtom>, AttrValueType>;
 
  protected: