Update DisplayLock lifecycle registration for top layer

WillStartLifecycleUpdate is only called when the DisplayLockContext is
subscribed to lifecycle updates, and the DisplayLockContext should only
be subscribed to lifecycle updates when NeedsLifecycleNotifications is
true. The DCHECK at the start of WillStartLifecycleUpdate enforces this.

has_pending_top_layer_check_ affects NeedsLifecycleNotifications, which
means that we need to unsubscribe from lifecycle notifications when it
becomes false. This patch adds a line of code to unsubscribe from
notifications when it is set to false.

Running slot-content-visibility-18-crash.html with --iterations=500 was
failing without this patch.

Fixed: 1367977
Change-Id: Ib5aa044d32e87f7dc7f4f8c9ed7cf08e979298ee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3923916
Reviewed-by: Vladimir Levin <vmpstr@chromium.org>
Commit-Queue: Joey Arhar <jarhar@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1052500}

third_party/blink/renderer/core/display_lock/display_lock_context.cc

@@ -855,6 +855,7 @@ void DisplayLockContext::WillStartLifecycleUpdate(const LocalFrameView& view) {
   if (has_pending_subtree_checks_ || has_pending_top_layer_check_) {
     DetermineIfSubtreeHasTopLayerElement();
     has_pending_top_layer_check_ = false;
+    update_registration = true;
   }
 
   if (has_pending_subtree_checks_) {