[DIAL] Make a copy of device id before erasing device from map.

chrome/browser/extensions/api/dial/dial_registry.cc

 // Copyright (c) 2012 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/extensions/api/dial/dial_registry.h"
 
 #include <memory>
 
 #include "base/memory/ptr_util.h"
 #include "base/stl_util.h"
@@ skipping 142 matching lines @@
 }
 
 bool DialRegistry::PruneExpiredDevices() {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   bool pruned_device = false;
   DeviceByLabelMap::iterator it = device_by_label_map_.begin();
   while (it != device_by_label_map_.end()) {
     auto* device = it->second;
     if (IsDeviceExpired(*device)) {
       VLOG(2) << "Device " << device->label() << " expired, removing";
-      const size_t num_erased_by_id =
-          device_by_id_map_.erase(device->device_id());
+
+      // Make a copy of the device ID here since |device| will be destroyed
+      // during erase().
+      std::string device_id = device->device_id();

[miu, 2016/10/22 18:37:19]

nit: Probably not a big deal for performance, but the copy can be avoided by
using std::move() here. Though, IIRC, our std::strings are ref-counted, so
there's probably no copy going on internally.

+      const size_t num_erased_by_id = device_by_id_map_.erase(device_id);

[Wez, 2016/10/22 00:55:39]

As discussed offline... wow, really surprised that std::map<> is so fragile :-(

       DCHECK_EQ(1U, num_erased_by_id);
       device_by_label_map_.erase(it++);
       pruned_device = true;
     } else {
       ++it;
     }
   }
   return pruned_device;
 }
 
@@ skipping 150 matching lines @@
     case NetworkChangeNotifier::CONNECTION_BLUETOOTH:
       if (!dial_) {
         VLOG(2) << "Connection detected, restarting discovery.";
         StartPeriodicDiscovery();
       }
       break;
   }
 }
 
 }  // namespace extensions