Update more ScopedObserver declarations.

All desktop Linux targets compile with ScopedObserver changes.

Bug: 998625
Change-Id: I40bb05e48a28a859cfdef67be6963f7cb473bf54
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1828289
Reviewed-by: Scott Violet <[email protected]>
Commit-Queue: Evan Stade <[email protected]>
Cr-Commit-Position: refs/heads/master@{#701760}
diff --git a/extensions/browser/process_manager.h b/extensions/browser/process_manager.h
index 22db482..37dc3c3 100644
--- a/extensions/browser/process_manager.h
+++ b/extensions/browser/process_manager.h
@@ -363,7 +363,7 @@
   // True if we have created the startup set of background hosts.
   bool startup_background_hosts_created_;
 
-  base::ObserverList<ProcessManagerObserver>::Unchecked observer_list_;
+  base::ObserverList<ProcessManagerObserver> observer_list_;
 
   // ID Counter used to set ProcessManager::BackgroundPageData close_sequence_id
   // members. These IDs are tracked per extension in background_page_data_ and