[Sync] Actively guard against provider being cleared in DeviceInfoSyncBridge.

components/sync/device_info/device_info_sync_bridge.cc

 // Copyright 2015 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_bridge.h"
 
 #include <stdint.h>
 
 #include <algorithm>
 #include <set>
@@ skipping 100 matching lines @@
 std::unique_ptr<MetadataChangeList>
 DeviceInfoSyncBridge::CreateMetadataChangeList() {
   return WriteBatch::CreateMetadataChangeList();
 }
 
 SyncError DeviceInfoSyncBridge::MergeSyncData(
     std::unique_ptr<MetadataChangeList> metadata_change_list,
     EntityDataMap entity_data_map) {
   DCHECK(has_provider_initialized_);
   DCHECK(change_processor()->IsTrackingMetadata());
+  const DeviceInfo* local_info =
+      local_device_info_provider_->GetLocalDeviceInfo();
+  // If our dependency was yanked out from beneath us, we cannot correctly
+  // handle this request, and all our data will be deleted soon.
+  if (local_info == nullptr) {
+    return SyncError();
+  }
 
   // Local data should typically be near empty, with the only possible value
   // corresponding to this device. This is because on signout all device info
   // data is blown away. However, this simplification is being ignored here and
   // a full difference is going to be calculated to explore what other bridge
   // implementations may look like.
   std::set<std::string> local_guids_to_put;
   for (const auto& kv : all_data_) {
     local_guids_to_put.insert(kv.first);
   }
 
   bool has_changes = false;
-  const DeviceInfo* local_info =
-      local_device_info_provider_->GetLocalDeviceInfo();
   std::string local_guid = local_info->guid();
   std::unique_ptr<WriteBatch> batch = store_->CreateWriteBatch();
   for (const auto& kv : entity_data_map) {
     const DeviceInfoSpecifics& specifics =
         kv.second.value().specifics.device_info();
     DCHECK_EQ(kv.first, specifics.cache_guid());
     if (specifics.cache_guid() == local_guid) {
       // Don't Put local data if it's the same as the remote copy.
       if (local_info->Equals(*SpecificsToModel(specifics))) {
         local_guids_to_put.erase(local_guid);
@@ skipping 14 matching lines @@
 
   batch->TransferMetadataChanges(std::move(metadata_change_list));
   CommitAndNotify(std::move(batch), has_changes);
   return SyncError();
 }
 
 SyncError DeviceInfoSyncBridge::ApplySyncChanges(
     std::unique_ptr<MetadataChangeList> metadata_change_list,
     EntityChangeList entity_changes) {
   DCHECK(has_provider_initialized_);
+  const DeviceInfo* local_info =
+      local_device_info_provider_->GetLocalDeviceInfo();
+  // If our dependency was yanked out from beneath us, we cannot correctly
+  // handle this request, and all our data will be deleted soon.
+  if (local_info == nullptr) {
+    return SyncError();
+  }
 
   std::unique_ptr<WriteBatch> batch = store_->CreateWriteBatch();
   bool has_changes = false;
   for (EntityChange& change : entity_changes) {
     const std::string guid = change.storage_key();
     // Each device is the authoritative source for itself, ignore any remote
     // changes that have our local cache guid.
-    if (guid == local_device_info_provider_->GetLocalDeviceInfo()->guid()) {
+    if (guid == local_info->guid()) {
       continue;
     }
 
     if (change.type() == EntityChange::ACTION_DELETE) {
       has_changes |= DeleteSpecifics(guid, batch.get());
     } else {
       const DeviceInfoSpecifics& specifics =
           change.data().specifics.device_info();
       DCHECK(guid == specifics.cache_guid());
       StoreSpecifics(base::MakeUnique<DeviceInfoSpecifics>(specifics),
@@ skipping 121 matching lines @@
   } else {
     return false;
   }
 }
 
 void DeviceInfoSyncBridge::OnProviderInitialized() {
   // Now that the provider has initialized, remove the subscription. The bridge
   // should only need to give the processor metadata upon initialization. If
   // sync is disabled and enabled, our provider will try to retrigger this
   // event, but we do not want to send any more metadata to the processor.
+  // TODO(skym, crbug.com/672600): Handle re-initialization and start the pulse
+  // timer.
   subscription_.reset();
 
   has_provider_initialized_ = true;
   LoadMetadataIfReady();
 }
 
 void DeviceInfoSyncBridge::OnStoreCreated(
     Result result,
     std::unique_ptr<ModelTypeStore> store) {
   if (result == Result::SUCCESS) {
@@ skipping 52 matching lines @@
   // On initial syncing we will have a change processor here, but it will not be
   // tracking changes. We need to persist a copy of our local device info to
   // disk, but the Put call to the processor will be ignored. That should be
   // fine however, as the discrepancy will be picked up later in merge. We don't
   // bother trying to track this case and act intelligently because simply not
   // much of a benefit in doing so.
   DCHECK(has_provider_initialized_);
 
   const DeviceInfo* current_info =
       local_device_info_provider_->GetLocalDeviceInfo();
+  // Must ensure |pulse_timer_| is started even if sync is in the process of
+  // being disabled. TODO(skym, crbug.com/672600): Remove this timer Start(), as
+  // it should be started when the provider re-initializes instead.
+  if (current_info == nullptr) {
+    pulse_timer_.Start(FROM_HERE, DeviceInfoUtil::kPulseInterval,
+                       base::Bind(&DeviceInfoSyncBridge::SendLocalData,
+                                  base::Unretained(this)));
+    return;
+  }
   auto iter = all_data_.find(current_info->guid());
 
   // Convert to DeviceInfo for Equals function.
   if (iter != all_data_.end() &&
       current_info->Equals(*SpecificsToModel(*iter->second))) {
     const TimeDelta pulse_delay(DeviceInfoUtil::CalculatePulseDelay(
         GetLastUpdateTime(*iter->second), Time::Now()));
     if (!pulse_delay.is_zero()) {
       pulse_timer_.Start(FROM_HERE, pulse_delay,
                          base::Bind(&DeviceInfoSyncBridge::SendLocalData,
@@ skipping 50 matching lines @@
 }
 
 void DeviceInfoSyncBridge::ReportStartupErrorToSync(const std::string& msg) {
   // TODO(skym): Shouldn't need to log this here, reporting should always log.
   LOG(WARNING) << msg;
   change_processor()->OnMetadataLoaded(
       change_processor()->CreateAndUploadError(FROM_HERE, msg), nullptr);
 }
 
 }  // namespace syncer