Mirror object for stack frames.
@param {number} break_id The break id in the VM for which this frame is
valid
@param {number} index The frame index (top frame is index 0)
@constructor
@extends Mirror
function FrameMirror(break_id, index) {
  %_Call(Mirror, this, MirrorType.FRAME_TYPE);
  this.break_id_ = break_id;
  this.index_ = index;
  this.details_ = new FrameDetails(break_id, index);
}