Fix DCHECK in network portal detector.

chrome/browser/chromeos/net/network_portal_detector_impl.cc

 // Copyright (c) 2013 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 "chrome/browser/chromeos/net/network_portal_detector_impl.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 531 matching lines @@
 
   if (result == captive_portal::RESULT_NO_RESPONSE)
     ++no_response_result_count_;
   else
     no_response_result_count_ = 0;
 
   if (state.status != CAPTIVE_PORTAL_STATUS_OFFLINE ||
       same_detection_result_count_ >= kMaxOfflineResultsBeforeReport) {
     OnDetectionCompleted(network, state);
   }
-  ScheduleAttempt(results.retry_after_delta);
+
+  // Observers (via OnDetectionCompleted) may already schedule new attempt.
+  if (is_idle())
+    ScheduleAttempt(results.retry_after_delta);
 }
 
 void NetworkPortalDetectorImpl::Observe(
     int type,
     const content::NotificationSource& source,
     const content::NotificationDetails& details) {
   if (type == chrome::NOTIFICATION_LOGIN_PROXY_CHANGED ||
       type == chrome::NOTIFICATION_AUTH_SUPPLIED ||
       type == chrome::NOTIFICATION_AUTH_CANCELLED) {
     NET_LOG(EVENT) << "Restarting portal detection due to proxy change"
@@ skipping 79 matching lines @@
 }
 
 void NetworkPortalDetectorImpl::ResetStrategyAndCounters() {
   last_detection_result_ = CAPTIVE_PORTAL_STATUS_UNKNOWN;
   same_detection_result_count_ = 0;
   no_response_result_count_ = 0;
   strategy_->Reset();
 }
 
 }  // namespace chromeos