Base class for all value mirror objects.
@param {string} type The type of the mirror
@param {value} value The value reflected by this mirror
@param {boolean} transient indicate whether this object is transient with a
transient handle
@constructor
@extends Mirror
function ValueMirror(type, value, transient) {
  %_Call(Mirror, this, type);
  this.value_ = value;
  if (!transient) {
    this.allocateHandle_();
  } else {
    this.allocateTransientHandle_();
  }
}