ash: Move AppList support to ShelfWidget, expose ShelfWidget in WmShelf

ash/shell_unittest.cc

Index: ash/shell_unittest.cc
diff --git a/ash/shell_unittest.cc b/ash/shell_unittest.cc
index 5ff61ff2981fc8698b0f9f60510e805303821906..1c40d69ac59ac79aa5bbe62deb46babe8f65317a 100644
--- a/ash/shell_unittest.cc
+++ b/ash/shell_unittest.cc
@@ -371,7 +371,7 @@ TEST_F(ShellTest, ManagedWindowModeBasics) {
   // We start with the usual window containers.
   ExpectAllContainers();
   // Shelf is visible.
-  ShelfWidget* shelf_widget = GetPrimaryShelf()->GetShelfWidgetForTesting();
+  ShelfWidget* shelf_widget = GetPrimaryShelf()->shelf_widget();
   EXPECT_TRUE(shelf_widget->IsVisible());
   // Shelf is at bottom-left of screen.
   EXPECT_EQ(0, shelf_widget->GetWindowBoundsInScreen().x());