Return the element representing the method that results from looking up
methodName in the superclass of this class with respect to the
library, ignoring abstract methods, or
null if the look up
fails. The behavior of this method is defined by the Dart Language
Specification in section 16.15.1:
The result of looking up method m in class C with respect to library L is: If C declares an instance method named m that is accessible to L, then that method is the result of the lookup. Otherwise, if C has a superclass S, then the result of the lookup is the result of looking up method m in S with respect to L. Otherwise, we say that the lookup has failed.
MethodElement lookUpInheritedConcreteMethod( String methodName, LibraryElement library);