[Extensions] Make const PermissionSet* const PermissionSet& where possible

Replace a bunch of pointers with const&.

[email protected] (themes)
[email protected] (background)
[email protected] (ui/sync)

BUG=455414

Review URL: https://codereview.chromium.org/1365443003

Cr-Commit-Position: refs/heads/master@{#351631}
diff --git a/apps/saved_files_service.cc b/apps/saved_files_service.cc
index 49e0b56f..43a0062 100644
--- a/apps/saved_files_service.cc
+++ b/apps/saved_files_service.cc
@@ -262,7 +262,7 @@
 void SavedFilesService::ClearQueueIfNoRetainPermission(
     const Extension* extension) {
   if (extensions::util::IsEphemeralApp(extension->id(), profile_) ||
-      !extension->permissions_data()->active_permissions()->HasAPIPermission(
+      !extension->permissions_data()->active_permissions().HasAPIPermission(
           APIPermission::kFileSystemRetainEntries)) {
     ClearQueue(extension);
   }