arc: Fix crash in arc_process_task.cc during browser shutdown

chrome/browser/task_manager/providers/arc/arc_process_task.cc

Index: chrome/browser/task_manager/providers/arc/arc_process_task.cc
diff --git a/chrome/browser/task_manager/providers/arc/arc_process_task.cc b/chrome/browser/task_manager/providers/arc/arc_process_task.cc
index e0b44c0825700c1fce30a2f988aab6f9e4d6840d..6b32713dd621529b5140de183f99e6bec2c4a1bd 100644
--- a/chrome/browser/task_manager/providers/arc/arc_process_task.cc
+++ b/chrome/browser/task_manager/providers/arc/arc_process_task.cc
@@ -113,10 +113,14 @@ void ArcProcessTask::StartIconLoading() {
 }
 
 ArcProcessTask::~ArcProcessTask() {
-  arc::ArcServiceManager::Get()
-      ->arc_bridge_service()
-      ->intent_helper()
-      ->RemoveObserver(this);
+  auto* service_manager = arc::ArcServiceManager::Get();
+  // This destructor can also be called when TaskManagerImpl is destructed.
+  // Since TaskManagerImpl is a LAZY_INSTANCE, arc::ArcServiceManager may have
+  // already been destructed. In that case, arc_bridge_service() has also been
+  // destructed, and it is safe to just return.
+  if (!service_manager)
+    return;
+  service_manager->arc_bridge_service()->intent_helper()->RemoveObserver(this);
 }
 
 Task::Type ArcProcessTask::GetType() const {