Enables delegating signal strategy for It2Me Host.

remoting/signaling/delegating_signal_strategy.h

Index: remoting/signaling/delegating_signal_strategy.h
diff --git a/remoting/client/plugin/delegating_signal_strategy.h b/remoting/signaling/delegating_signal_strategy.h
similarity index 57%
rename from remoting/client/plugin/delegating_signal_strategy.h
rename to remoting/signaling/delegating_signal_strategy.h
index 9a9096f44a5d1cb49fbeb7891a2fccb8269d5339..184394db95f9f89df1b0e187b4046fb288a3762b 100644
--- a/remoting/client/plugin/delegating_signal_strategy.h
+++ b/remoting/signaling/delegating_signal_strategy.h
@@ -7,7 +7,8 @@
 
 #include "base/callback.h"
 #include "base/macros.h"
-#include "base/observer_list.h"
+#include "base/memory/weak_ptr.h"
+#include "base/observer_list_threadsafe.h"
 #include "remoting/signaling/signal_strategy.h"
 
 namespace base {
@@ -16,12 +17,24 @@ class SingleThreadTaskRunner;
 
 namespace remoting {
 
+// A signaling strategy class that delegates IQ sending and receiving.
+//
+// Notes on thread safety:
+// 1. This object can be created on any thread.
+// 2. OnIncomingMessage() and |send_iq_callback| will always be called on the

[Sergey Ulanov, 2016/10/06 18:28:57]

Suggest separating this statement into two. |send_iq_callback| is called by this
class, while  OnIncomingMessage() will be called by the client. I.e. add a new
item between (2) and (3): OnIncomingMessage() must be called on the same same
thread on which this object is created.

[kelvinp, 2016/10/06 20:30:28]

Done.

+//    thread that it is created on. Note that |send_iq_callback| may be called
+//    after the instance is destroyed.
+// 3. The caller should invoke all methods on the |client_task_runner|.

[Sergey Ulanov, 2016/10/06 18:28:57]

Maybe rephrase this as "SignalStrategy interface must be used on
|client_task_runner|."

[kelvinp, 2016/10/06 20:30:28]

Done.

+// 4. All listeners will be called on |client_task_runner| as well.
+// 5. The destructor should always be called on the |client_task_runner|.
 class DelegatingSignalStrategy : public SignalStrategy {
  public:
   typedef base::Callback<void(const std::string&)> SendIqCallback;
 
-  DelegatingSignalStrategy(std::string local_jid,
-                       const SendIqCallback& send_iq_callback);
+  DelegatingSignalStrategy(
+      std::string local_jid,
+      scoped_refptr<base::SingleThreadTaskRunner> client_task_runner,
+      const SendIqCallback& send_iq_callback);
   ~DelegatingSignalStrategy() override;
 
   void OnIncomingMessage(const std::string& message);
@@ -39,10 +52,14 @@ class DelegatingSignalStrategy : public SignalStrategy {
 
  private:
   std::string local_jid_;
-  SendIqCallback send_iq_callback_;
+  scoped_refptr<base::SingleThreadTaskRunner> delegate_task_runner_;
+  scoped_refptr<base::SingleThreadTaskRunner> client_task_runner_;
 
+  SendIqCallback send_iq_callback_;
   base::ObserverList<Listener> listeners_;
 
+  base::WeakPtrFactory<DelegatingSignalStrategy> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(DelegatingSignalStrategy);
 };