Better handle session start in AppListControllerImpl

A folow-up on CL:1988989 with a couple of things I realized can be done
better:
*   use presenter_.GetTargetVisibility() to check if app list has been
    previously shown
*   Show app list in tablet mode using HomeScreenController::Show (it
    handles some additional tablet mode specific things - e.g. sets the
    show source)
*   Use last_target_visible_ to check if app list should be visible when
    session changes to active (instead of trying to recalculate target
    visibility state again)

BUG=1038512

Change-Id: I6a1aa7613935ed042a45b4aa622bd7cf2203a071
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1992242Reviewed-by: Alex Newcomer <newcomer@chromium.org>
Commit-Queue: Toni Baržić <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#729962}

ash/app_list/app_list_controller_impl.cc

@@ -511,15 +511,12 @@ void AppListControllerImpl::OnSessionStateChanged(
   // Show the app list after signing in in tablet mode. For metrics, the app
   // list is not considered shown since the browser window is shown over app
   // list upon login.
-  if (!presenter_.GetView()) {
-    Show(GetDisplayIdToShowAppListOn(),
-         base::nullopt /* no AppListShowSource */, base::TimeTicks());
-  }
+  if (!presenter_.GetTargetVisibility())
+    Shell::Get()->home_screen_controller()->Show();
 
   // Hide app list UI initially to prevent app list from flashing in background
   // while the initial app window is being shown.
-  if (HasVisibleWindows() ||
-      Shell::Get()->overview_controller()->InOverviewSession()) {
+  if (!last_target_visible_) {
     presenter_.GetView()->SetVisible(false);
     presenter_.GetView()->search_box_view()->SetVisible(false);
   } else {