Reset holding space model before calling detach observers

Resets current holding space model before calling holding space
detached, so HoldingSpaceController::Get()->model() can be used
test whether a model is currently attached from the observer method.

Also, updates HoldingSpaceTray to cancel previews update when previews
icon gets hidden.

BUG=1164145

Change-Id: I1f0b50cc52c5b348b0e034e65751b9a0047bd096
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2618093Reviewed-by: David Black <dmblack@google.com>
Commit-Queue: Toni Baržić <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841691}

ash/public/cpp/holding_space/holding_space_controller.cc

@@ -83,8 +83,10 @@ void HoldingSpaceController::SetClient(HoldingSpaceClient* client) {
 
 void HoldingSpaceController::SetModel(HoldingSpaceModel* model) {
   if (model_) {
+    HoldingSpaceModel* const old_model = model_;
+    model_ = nullptr;
     for (auto& observer : observers_)
-      observer.OnHoldingSpaceModelDetached(model_);
+      observer.OnHoldingSpaceModelDetached(old_model);
   }
 
   model_ = model;

ash/system/holding_space/holding_space_tray.cc

@@ -195,12 +195,16 @@ void HoldingSpaceTray::SetVisiblePreferred(bool preferred_visibility) {
   }
 }
 
+void HoldingSpaceTray::FirePreviewsUpdateTimerIfRunningForTesting() {
+  if (previews_update_.IsRunning())
+    previews_update_.FireNow();
+}
+
 void HoldingSpaceTray::UpdateVisibility() {
   HoldingSpaceModel* model = HoldingSpaceController::Get()->model();
   LoginStatus login_status = shelf()->GetStatusAreaWidget()->login_status();
   const bool in_active_session = login_status != LoginStatus::NOT_LOGGED_IN &&
                                  login_status != LoginStatus::LOCKED;
-
   if (!model || !in_active_session) {
     SetVisiblePreferred(false);
     return;
@@ -378,6 +382,9 @@ void HoldingSpaceTray::UpdatePreviewsVisibility() {
 
   DCHECK(previews_tray_icon_);
   previews_tray_icon_->SetVisible(show_previews);
+
+  if (!show_previews)
+    previews_update_.Stop();
 }
 
 void HoldingSpaceTray::SchedulePreviewsIconUpdate() {

ash/system/holding_space/holding_space_tray.h

@@ -72,6 +72,8 @@ class ASH_EXPORT HoldingSpaceTray : public TrayBackgroundView,
     use_zero_previews_update_delay_ = zero_delay;
   }
 
+  void FirePreviewsUpdateTimerIfRunningForTesting();
+
  private:
   void UpdateVisibility();