InputDispatcher: Look up channel by token.

When comparing InputChannels coming from the client (for example to see if
a connection has dissapeared in the latest list), we need to compare by token
not by equality since of course they will now be different objects
each call to setInputWindows.

Bug: 80101428
Bug: 113136004
Bug: 111440400
Test: Manual
Change-Id: Ic384822df8418c80fb5578213149863044f890f4