Change the timing of Hide and losing Focus in Mash

This CL changes the order of HideImpl and giving up the focus
within DesktopWindowTreeHostMus. As is written in the comment,
this is because some code like WindowActivityWatcher assumes
the window is already invisible when the window gives up the
focus.

BUG=896080
TEST=interactive_ui_tests --enable-features=SingleProcessMash

Change-Id: I48a45bbea87c2e66d9827d2f7776b038edfca512
Reviewed-on: https://chromium-review.googlesource.com/c/1297401Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Jun Mukai <mukai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#602245}

testing/buildbot/filters/chromeos.single_process_mash.interactive_ui_tests.filter

@@ -10,9 +10,6 @@
 
 # misc.
 -DevToolsManagerDelegateTest.ShowMinimizedWindow
--WindowActivityWatcherTest.Basic
--WindowActivityWatcherTest.MultipleWindows
--WindowActivityWatcherTest.WindowActivation
 
 # Broken tests related to accessibility. crbug.com/888750 and crbug.com/889093
 -GuestSpokenFeedbackTest.FocusToolbar

ui/views/mus/desktop_window_tree_host_mus.cc

@@ -903,19 +903,22 @@ void DesktopWindowTreeHostMus::ShowImpl() {
 }
 
 void DesktopWindowTreeHostMus::HideImpl() {
+  native_widget_delegate_->OnNativeWidgetVisibilityChanging(false);
+  WindowTreeHostMus::HideImpl();
+  native_widget_delegate_->OnNativeWidgetVisibilityChanged(false);
+
   // When hiding we can't possibly be active any more. Reset the FocusClient,
   // which effectively triggers giving up focus (and activation). Mus will
-  // eventually generate a focus event, but that's async.
+  // eventually generate a focus event, but that's async. This should be done
+  // after the window gets hidden actually, since some code (like
+  // WindowActivityWatcher) assumes closing window is already invisible when the
+  // focus is lost. See https://crbug.com/896080.
   if (IsFocusClientInstalledOnFocusSynchronizer()) {
     MusClient::Get()
         ->window_tree_client()
         ->focus_synchronizer()
         ->SetActiveFocusClient(nullptr, nullptr);
   }
-
-  native_widget_delegate_->OnNativeWidgetVisibilityChanging(false);
-  WindowTreeHostMus::HideImpl();
-  native_widget_delegate_->OnNativeWidgetVisibilityChanged(false);
 }
 
 void DesktopWindowTreeHostMus::SetBoundsInPixels(