@Nullable ExecutableElement methodFromSuperclasses(TypeElement in, ExecutableElement method) {
      for (TypeElement t = in; t != null; t = superclass(t)) {
        ExecutableElement tMethod = methodInType(t, method);
        if (tMethod != null) {
          return tMethod;
        }
      }
      return null;
    }
Returns the given method as it appears in the given type. This is the method itself, or the
nearest override in a superclass of the given type, or null if the method is not found in the
given type or any of its superclasses.
common/src/main/java/com/google/auto/common/Overrides.java