Update dispatcher_host.cc

Was getting spammed with all these logs in the terminal:
[24098:0402/164715:WARNING:dispatcher_host.cc(196)] Unknown object: 1 type:Window method:ShowDevTools arguments:[ "", false ]
[24098:0402/164727:WARNING:dispatcher_host.cc(196)] Unknown object: 2 type:Window method:GetPosition arguments:[  ]
[24098:0402/164727:WARNING:dispatcher_host.cc(196)] Unknown object: 2 type:Window method:GetPosition arguments:[  ]
[24098:0402/164727:WARNING:dispatcher_host.cc(196)] Unknown object: 2 type:Window method:GetSize arguments:[  ]
[24098:0402/164727:WARNING:dispatcher_host.cc(196)] Unknown object: 2 type:Window method:GetSize arguments:[  ]

Fixed this by borrowing the same flow as DispatcherHost::OnCallObjectMethod (line 178).
Merge pull request #1748 from Ziugy/master

Fixing inaccurate warning logging when accessing properties on windows.