public void onRelationshipValidationResult(@Relation int relation, Uri requestedOrigin,
                                               boolean result, Bundle extras) {}
Called when a relationship validation result is available.

@param relation Relation for which the result is available. Value previously passed to
                {@link CustomTabsSession#validateRelationship(int, Uri, Bundle)}. Must be one
                of the {@code CustomTabsService#RELATION_* } constants.
@param requestedOrigin Origin requested. Value previously passed to
                       {@link CustomTabsSession#validateRelationship(int, Uri, Bundle)}.
@param result Whether the relation was validated.
@param extras Reserved for future use.
customtabs/src/android/support/customtabs/CustomTabsCallback.java