[Remoting Android] Move pairing secret fetcher to the network thread

remoting/client/jni/jni_pairing_secret_fetcher.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef REMOTING_CLIENT_JNI_JNI_PAIRING_SECRET_FETCHER_H_
 #define REMOTING_CLIENT_JNI_JNI_PAIRING_SECRET_FETCHER_H_
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "remoting/protocol/client_authentication_config.h"
 
 namespace remoting {
 
 class ChromotingJniRuntime;
 class JniClient;
 
-// This class fetches the pairing secret on the UI thread. It must be deleted
-// on UI.
+// This class fetches the pairing secret on the UI thread. This should be
+// created on the UI thread but there after used and deleted on the network
+// thread.
 class JniPairingSecretFetcher {
  public:
   JniPairingSecretFetcher(ChromotingJniRuntime* runtime,
                    base::WeakPtr<JniClient> client,
                    const std::string& host_id);
   virtual ~JniPairingSecretFetcher();
 
-  // Called on UI thread. Notifies the user interface that the user needs to
-  // enter a PIN. The current authentication attempt is put on hold until
-  // |callback| is invoked. |callback| will be run on the network thread.
+  // Notifies the user interface that the user needs to enter a PIN. The current
+  // authentication attempt is put on hold until |callback| is invoked.
   void FetchSecret(bool pairable,
                    const protocol::SecretFetchedCallback& callback);
 
   // Provides the user's PIN and resumes the host authentication attempt. Call
-  // on the UI thread once the user has finished entering this PIN into the UI,
-  // but only after the UI has been asked to provide a PIN (via FetchSecret()).
+  // once the user has finished entering this PIN into the UI, but only after
+  // the UI has been asked to provide a PIN (via FetchSecret()).
   void ProvideSecret(const std::string& pin);
 
-  // Get weak pointer to be used on the UI thread.
+  // Get weak pointer to be used on the network thread.
   base::WeakPtr<JniPairingSecretFetcher> GetWeakPtr();
 
  private:
+  static void FetchSecretOnUiThread(base::WeakPtr<JniClient> client,
+                                    const std::string& host_id,
+                                    bool pairable);
+
   ChromotingJniRuntime* jni_runtime_;
   base::WeakPtr<JniClient> jni_client_;
 
   std::string host_id_;
 
   // Pass this the user's PIN once we have it. To be assigned and accessed on
   // the UI thread, but must be posted to the network thread to call it.
   protocol::SecretFetchedCallback callback_;
 
   base::WeakPtrFactory<JniPairingSecretFetcher> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(JniPairingSecretFetcher);
 };
 
 }  // namespace remoting
 
 #endif  // REMOTING_CLIENT_JNI_JNI_PAIRING_SECRET_FETCHER_H_