public final boolean up(VM_StackBrowser browser) { return false; }
  public final void set(VM_StackBrowser browser, int instr) {    if (VM.VerifyAssertions) VM.assert(VM.NOT_REACHED);  }         /**   * Advance the VM_StackBrowser up one internal stack frame, if possible   */  public final boolean up(VM_StackBrowser browser) {    return false;  }