public int defineTokenName(String name, int ttype) {
		Integer prev = tokenNameToTypeMap.get(name);
		if ( prev!=null ) return prev;
		tokenNameToTypeMap.put(name, ttype);
		setTokenForType(ttype, name);
		maxTokenType = Math.max(maxTokenType, ttype);
		return ttype;
	}
Return a new unique integer in the channel value space.
tool/src/org/antlr/v4/tool/Grammar.java