Prevent tab focus moved onto buttons not visible in collapsed mode.

Test: manually verified
Bug: 858957
Change-Id: I31c2b69ca92680ea38ab38ba65f13169e0e11b45
Reviewed-on: https://chromium-review.googlesource.com/1128822Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Commit-Queue: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574097}

ash/system/unified/feature_pods_container_view.cc

@@ -84,6 +84,11 @@ void FeaturePodsContainerView::ChildVisibilityChanged(View* child) {
   SchedulePaint();
 }
 
+void FeaturePodsContainerView::ViewHierarchyChanged(
+    const ViewHierarchyChangedDetails& details) {
+  UpdateChildVisibility();
+}
+
 void FeaturePodsContainerView::Layout() {
   UpdateCollapsedSidePadding();
 

ash/system/unified/feature_pods_container_view.h

@@ -36,6 +36,8 @@ class ASH_EXPORT FeaturePodsContainerView : public views::View {
   // Overridden views::View:
   gfx::Size CalculatePreferredSize() const override;
   void ChildVisibilityChanged(View* child) override;
+  void ViewHierarchyChanged(
+      const ViewHierarchyChangedDetails& details) override;
   void Layout() override;
 
  private: