Add unit tests for home launcher

BUG=835012

Change-Id: Ib59301c4ef4aece078daaa41aa3ce4fb0639e8c8
Reviewed-on: https://chromium-review.googlesource.com/1022710
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552796}

ui/app_list/views/app_list_view.cc

@@ -1044,10 +1044,12 @@ void AppListView::OnTabletModeChanged(bool started) {
 
     // Put app list window in corresponding container based on whether the
     // tablet mode is enabled.
-    aura::Window* root_window = GetWidget()->GetNativeView()->GetRootWindow();
     aura::Window* window = GetWidget()->GetNativeWindow();
-    root_window->GetChildById(ash::kShellWindowId_AppListTabletModeContainer)
-        ->AddChild(window);
+    aura::Window* root_window = window->GetRootWindow();
+    aura::Window* parent_window = root_window->GetChildById(
+        ash::kShellWindowId_AppListTabletModeContainer);
+    if (!parent_window->Contains(window))
+      parent_window->AddChild(window);
 
     // Update background opacity.
     app_list_background_shield_->layer()->SetOpacity(

ui/app_list/views/app_list_view.h

@@ -233,6 +233,10 @@ class APP_LIST_EXPORT AppListView : public views::WidgetDelegateView,
   // Returns true if the home launcher is enabled in tablet mode.
   bool IsHomeLauncherEnabledInTabletMode() const;
 
+  views::View* app_list_background_shield_for_test() {
+    return app_list_background_shield_;
+  }
+
  private:
   // A widget observer that is responsible for keeping the AppListView state up
   // to date on closing.