Adding ThreadChecker validation to d'tors for client classes

remoting/client/chromoting_client.cc

Index: remoting/client/chromoting_client.cc
diff --git a/remoting/client/chromoting_client.cc b/remoting/client/chromoting_client.cc
index 802947708381afbbcaf4120ba78eed7fa60831a9..ced714a15bee00df6e9a2175c49e75b99de64d2d 100644
--- a/remoting/client/chromoting_client.cc
+++ b/remoting/client/chromoting_client.cc
@@ -40,6 +40,8 @@ ChromotingClient::ChromotingClient(
 }
 
 ChromotingClient::~ChromotingClient() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
   if (signal_strategy_)
       signal_strategy_->RemoveListener(this);
 }