Reland enable VK overscroll by default. Fixed ash unittest.

ash/root_window_controller_unittest.cc

Index: ash/root_window_controller_unittest.cc
diff --git a/ash/root_window_controller_unittest.cc b/ash/root_window_controller_unittest.cc
index 803e07800cc4df25db5843db938d5ec979864b2c..3edd28013e160131fde6d374312f1c40f5da724c 100644
--- a/ash/root_window_controller_unittest.cc
+++ b/ash/root_window_controller_unittest.cc
@@ -714,8 +714,10 @@ TEST_F(VirtualKeyboardRootWindowControllerTest, RestoreWorkspaceAfterLogin) {
   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();