code: public JSModule getDeepestCommonDependencyInclusive(
        JSModule m1, JSModule m2) {
      if (m2 == m1 || dependsOn(m2, m1)) {
        return m1;
      } else if (dependsOn(m1, m2)) {
        return m2;
      }
  
      return getDeepestCommonDependency(m1, m2);
    }
docs: Finds the deepest common dependency of two modules, including the
  modules themselves.
  
  @param m1 A module in this graph
  @param m2 A module in this graph
  @return The deepest common dep of {@code m1} and {@code m2}, or null if
  they have no common dependencies