Removed IPC and fixed isClosed property checks in SESession and SEChannel

+ removed IPC in get isClosed()
+ _isClosed in chromeObj stores the info in content process
+ _stateInfoMap now stores chromeObjs instead of contentObjs (need to be able to change _isClosed on session/channel removal)
+ chromeObj._contentObj stores the reference to content obj (for the purpose of linking between channel and session)