cros: Center the OOBE dialog in the work area instead of the whole screen

This makes the views-login dialog more consistent with how the webui version looks.

Change-Id: I1c931623ae9c8b6408debe315ab7cac8d4cac742
Reviewed-on: https://chromium-review.googlesource.com/1162745Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Commit-Queue: Quan Nguyen <qnnguyen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580661}

chrome/browser/chromeos/login/ui/oobe_ui_dialog_delegate.cc

@@ -137,7 +137,7 @@ void OobeUIDialogDelegate::UpdateSizeAndPosition(int width, int height) {
   gfx::Rect display_rect =
       display::Screen::GetScreen()
           ->GetDisplayNearestWindow(dialog_widget_->GetNativeWindow())
-          .bounds();
+          .work_area();
 
   // Place the dialog in the center of the screen.
   const gfx::Rect bounds(