Bug 1628715 - Part 14: Add MOZ_NONNULL_RETURN attribute on NotNull::operator->. r=jwalden

Differential Revision: https://phabricator.services.mozilla.com/D71299

mfbt/NotNull.h

@@ -140,7 +140,9 @@ class NotNull {
   constexpr operator const T&() const { return get(); }
 
   // Dereference operators.
-  constexpr const T& operator->() const { return get(); }
+  constexpr auto* operator->() const MOZ_NONNULL_RETURN {
+    return mBasePtr.operator->();
+  }
   constexpr decltype(*mBasePtr) operator*() const { return *mBasePtr; }
 };