Review

class JSTypeRegistry {
  /**
   * Tells the type system that {@code owner} may have a property named
   * {@code propertyName}. This allows the registry to keep track of what
   * types a property is defined upon.
   *
   * This is NOT the same as saying that {@code owner} must have a property
   * named type. ObjectType#hasProperty attempts to minimize false positives
   * ("if we're not sure, then don't type check this property"). The type
   * registry, on the other hand, should attempt to minimize false negatives
   * ("if this property is assigned anywhere in the program, it must
   * show up in the type registry").
   */
  public void registerPropertyOnType(String propertyName, JSType type) {
    UnionTypeBuilder typeSet = typesIndexedByProperty.get(propertyName);
    if (typeSet == null) {
      typeSet = new UnionTypeBuilder(this);
      typesIndexedByProperty.put(propertyName, typeSet);
    }

    typeSet.addAlternate(type);
    addReferenceTypeIndexedByProperty(propertyName, type);

    // Clear cached values that depend on typesIndexedByProperty.
    greatestSubtypeByProperty.remove(propertyName);
  }

}