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

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

Index: chrome/browser/extensions/api/dial/dial_registry.cc
diff --git a/chrome/browser/extensions/api/dial/dial_registry.cc b/chrome/browser/extensions/api/dial/dial_registry.cc
index 3c092bdeee1742acf17179c8ba6810ee9ae31797..f3cbe46ef07475adb6df57c9d42e37b5493ab561 100644
--- a/chrome/browser/extensions/api/dial/dial_registry.cc
+++ b/chrome/browser/extensions/api/dial/dial_registry.cc
@@ -160,8 +160,11 @@ bool DialRegistry::PruneExpiredDevices() {
     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;