code: public int getSourceOffset() {
      StaticSourceFile file = getStaticSourceFile();
      if (file == null) {
        return -1;
      }
      int lineno = getLineno();
      if (lineno == -1) {
        return -1;
      }
      return file.getLineOffset(lineno) + getCharno();
    }
docs: TODO(johnlenz): make this final