Reland enable VK overscroll by default. Fixed ash unittest.

ash/root_window_controller_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/root_window_controller.h"
 
 #include "ash/session/session_state_delegate.h"
 #include "ash/shelf/shelf_layout_manager.h"
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
@@ skipping 696 matching lines @@
   keyboard_window->SetBounds(keyboard::KeyboardBoundsFromWindowBounds(
       keyboard_container->bounds(), 100));
   keyboard_window->Show();
 
   gfx::Rect before = ash::Shell::GetScreen()->GetPrimaryDisplay().work_area();
 
   // Notify keyboard bounds changing.
   controller->NotifyKeyboardBoundsChanging(
       controller->proxy()->GetKeyboardWindow()->bounds());
 
-  gfx::Rect after = ash::Shell::GetScreen()->GetPrimaryDisplay().work_area();
-  EXPECT_LT(after, before);
+  if (!keyboard::IsKeyboardOverscrollEnabled()) {
+    gfx::Rect after = ash::Shell::GetScreen()->GetPrimaryDisplay().work_area();
+    EXPECT_LT(after, before);
+  }
 
   // Mock a login user profile change to reinitialize the keyboard.
   ash::Shell::GetInstance()->OnLoginUserProfilePrepared();
   EXPECT_EQ(ash::Shell::GetScreen()->GetPrimaryDisplay().work_area(), before);
 }
 
 // Ensure that system modal dialogs do not block events targeted at the virtual
 // keyboard.
 TEST_F(VirtualKeyboardRootWindowControllerTest, ClickWithActiveModalDialog) {
   aura::Window* root_window = Shell::GetPrimaryRootWindow();
@@ skipping 30 matching lines @@
   modal_widget->Close();
 
   // Verify that mouse events are now unblocked to the root window.
   root_window_event_generator.ClickLeftButton();
   EXPECT_EQ(2, handler.num_mouse_events() / 2);
   root_window->RemovePreTargetHandler(&handler);
 }
 
 }  // namespace test
 }  // namespace ash