code: private void handleParentMethod(ExecutableElement parentMethodElement, ExecutableElement
        childMethodElement) {
      MethodReferenceNode parentMethodNode = (MethodReferenceNode) elementReferenceMap
          .get(stitchMethodIdentifier(parentMethodElement));
      if (parentMethodNode == null) {
        parentMethodNode = new MethodReferenceNode(parentMethodElement);
      }
      parentMethodNode.invokedMethods.add(stitchMethodIdentifier(childMethodElement));
      elementReferenceMap.put(stitchMethodIdentifier(parentMethodElement), parentMethodNode);
      addToOverrideMap(parentMethodElement);
    }
docs: Adds a node for the parent in the elementReferenceMap if it doesn't exist, adds the method to
  the override map, and links the child method in the invokedMethods set.
  @param parentMethodElement
  @param childMethodElement