Add ProtoAware to change detection

[mhevery]

In order to support ng-repeat and to not have ProtoMap which forwards to parent map we need a class which can at 'compile-time' answer if we can dereference a nam.

abstract class ProtoAware {
  Object parent;
  bool hasProperty(String name);
  operator[] 
}

This way a repeater can define:

class RepeatContext extends ProtoAware {
  Object parent;
  String itemName;
  hasProperty(name) => name == itemName || name == '$index';
}

This way the change detection system on assignment can query the object and determine if the object understand a field. If it does not it checks the parent. This way it is possible to emulate prototypical inheritance without reflection.

[chalin]

Nice.