CrOS app list: Apply the parallel tweak to app list _target visibility_

This applies the same change made in CL 1814222 (for the _visibility_
chain of events), to the _target visibility_ chain of events and
observers.

This fixes tests that are failing with pending CL 1832634.

Bug: 1006013
Change-Id: I6992f16d79393b16d3813090ec3d69090335fe14
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1834653
Commit-Queue: Manu Cornet <manucornet@chromium.org>
Reviewed-by: Alex Newcomer <newcomer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#702062}

ash/app_list/app_list_controller_impl.cc

@@ -1296,15 +1296,17 @@ void AppListControllerImpl::NotifyAppListTargetVisibilityChanged(
   }
 
   // Notify chrome of target visibility changes.
-  if (client_)
-    client_->OnAppListTargetVisibilityChanged(real_target_visibility);
-
-  for (auto& observer : observers_)
-    observer.OnAppListTargetVisibilityChanged(real_target_visibility,
-                                              display_id);
+  if (last_target_visible_ != real_target_visibility) {
+    if (client_)
+      client_->OnAppListTargetVisibilityChanged(real_target_visibility);
 
-  last_target_visible_ = real_target_visibility;
-  last_target_visible_display_id_ = display_id;
+    for (auto& observer : observers_) {
+      observer.OnAppListTargetVisibilityChanged(real_target_visibility,
+                                                display_id);
+    }
+    last_target_visible_ = real_target_visibility;
+    last_target_visible_display_id_ = display_id;
+  }
 }
 
 ////////////////////////////////////////////////////////////////////////////////