This class provides an empty implementation of Java8Visitor,
which can be extended to create a visitor which only needs to handle a subset
of the available methods.
To detect from GWT java files new I18n keys, says content of patterns :
@Key("XXX")@LocalizableResource.Key("XXX")@com.google.gwt.i18n.client.LocalizableResource.Key("XXX")Note: this goal must always be invoked before the process-resources
phase, otherwise all files will be considered as uptodate.