[Sync] Always check the device info provider for being null before using it.

components/sync/device_info/device_info_sync_service.cc

 // Copyright 2014 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 "components/sync/device_info/device_info_sync_service.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <utility>
@@ skipping 267 matching lines @@
   }
 }
 
 void DeviceInfoSyncService::SendLocalData(
     const SyncChange::SyncChangeType change_type) {
   DCHECK_NE(change_type, SyncChange::ACTION_INVALID);
   DCHECK(sync_processor_);
 
   const DeviceInfo* device_info =
       local_device_info_provider_->GetLocalDeviceInfo();
-  const SyncData& data = CreateLocalData(device_info);
-  StoreSyncData(device_info->guid(), data);
 
-  SyncChangeList change_list;
-  change_list.push_back(SyncChange(FROM_HERE, change_type, data));
-  sync_processor_->ProcessSyncChanges(FROM_HERE, change_list);
+  // While the |pulse_timer_| is shutdown eventually in StopSyncing(), our
+  // device info provider is ripped out from underneath us before that happens,
+  // and we need to guard against this.
+  if (device_info != nullptr) {
+    const SyncData& data = CreateLocalData(device_info);
+    StoreSyncData(device_info->guid(), data);
+
+    SyncChangeList change_list;
+    change_list.push_back(SyncChange(FROM_HERE, change_type, data));
+    sync_processor_->ProcessSyncChanges(FROM_HERE, change_list);
+  }
 
   pulse_timer_.Start(
       FROM_HERE, DeviceInfoUtil::kPulseInterval,
       base::Bind(&DeviceInfoSyncService::SendLocalData, base::Unretained(this),
                  SyncChange::ACTION_UPDATE));
 }
 
 int DeviceInfoSyncService::CountActiveDevices(const Time now) const {
   return std::count_if(all_data_.begin(), all_data_.end(),
                        [now](SyncDataMap::const_reference pair) {
@@ skipping 12 matching lines @@
     return SyncDataRemote(device_info).GetModifiedTime();
   } else {
     // We shouldn't reach this point for remote data, so this means we're likely
     // looking at the local device info. Using a long ago time is perfect, since
     // the desired behavior is to update/pulse our data as soon as possible.
     return Time();
   }
 }
 
 }  // namespace syncer