[Remoting Android] Fix GetWeakPtr() calls on multiple threads

remoting/client/jni/jni_pairing_secret_fetcher.cc

 // 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.
 
 #include "remoting/client/jni/jni_pairing_secret_fetcher.h"
 #include "base/bind.h"
 #include "base/location.h"
 #include "remoting/client/jni/chromoting_jni_runtime.h"
 #include "remoting/client/jni/jni_client.h"
 
 namespace remoting {
 
 JniPairingSecretFetcher::JniPairingSecretFetcher(ChromotingJniRuntime* runtime,
                                    base::WeakPtr<JniClient> client,
                                    const std::string& host_id) :
     jni_runtime_(runtime),
     jni_client_(client),
     host_id_(host_id),
-    weak_factory_(this) {}
+    weak_factory_(this) {
+  weak_ptr_ = weak_factory_.GetWeakPtr();
+}
 
 JniPairingSecretFetcher::~JniPairingSecretFetcher() {
   DCHECK(jni_runtime_->network_task_runner()->BelongsToCurrentThread());
 }
 
 void JniPairingSecretFetcher::FetchSecret(
     bool pairable,
     const protocol::SecretFetchedCallback& callback) {
   DCHECK (jni_runtime_->network_task_runner()->BelongsToCurrentThread());
 
   callback_ = callback;
   jni_runtime_->ui_task_runner()->PostTask(
       FROM_HERE,
       base::Bind(&JniPairingSecretFetcher::FetchSecretOnUiThread, jni_client_,
                  host_id_, pairable));
 }
 
 void JniPairingSecretFetcher::ProvideSecret(const std::string& pin) {
   DCHECK(jni_runtime_->network_task_runner()->BelongsToCurrentThread());
   DCHECK(!callback_.is_null());
 
   callback_.Run(pin);
 }
 
 base::WeakPtr<JniPairingSecretFetcher> JniPairingSecretFetcher::GetWeakPtr() {
-  return weak_factory_.GetWeakPtr();
+  return weak_ptr_;
 }
 
 // static
 void JniPairingSecretFetcher::FetchSecretOnUiThread(
     base::WeakPtr<JniClient> client,
     const std::string& host_id,
     bool pairable) {
   if (!client) {
     return;
   }
 
   // Delete pairing credentials if they exist.
   client->CommitPairingCredentials(host_id, "", "");
 
   client->DisplayAuthenticationPrompt(pairable);
 }
 
 }  // namespace remoting