Adding ThreadChecker validation to d'tors for protocol classes

There was an incorrect assumption about how ThreadChecker worked which lead
to several classes not having the d'tor guarantees they expected.  The
assumption was that a ThreadChecker would DCHECK if it was not destroyed on
the same thread it was bound to.  This is not correct so I am adding DCHECKs
to the d'tors of the remoting classes which were missed.

BUG=715633

Review-Url: https://codereview.chromium.org/2890833002
Cr-Commit-Position: refs/heads/master@{#472507}
diff --git a/remoting/protocol/channel_socket_adapter.cc b/remoting/protocol/channel_socket_adapter.cc
index 4d727f5..7e22b67 100644
--- a/remoting/protocol/channel_socket_adapter.cc
+++ b/remoting/protocol/channel_socket_adapter.cc
@@ -28,6 +28,7 @@
 }
 
 TransportChannelSocketAdapter::~TransportChannelSocketAdapter() {
+  DCHECK(thread_checker_.CalledOnValidThread());
   if (!destruction_callback_.is_null())
     destruction_callback_.Run();
 }