Summary:
Adds the possibility to define agents in Javascript. Javascript agents are simple classes that extend `InspectorAgent` and pass down the
given `EventSender` to the super constructor. The library will then call methods on the object for each received method call over the protocol.
Reviewed By: davidaurelio
Differential Revision: D4021508
fbshipit-source-id: bbe609e92ea726cbbbec833df81705ebd3346c77
Alexander Blom