[Harmony Cast Dialog] Update the scroll bar position for the sink list

When we restore the scroll position after a model update, we must
refresh the scroll view layout to show the scroll bar in the right
position.

Bug: 848974
Change-Id: I20748614d5c594efb472e5cd19d9c7a823fa483b
Reviewed-on: https://chromium-review.googlesource.com/1157558Reviewed-by: Derek Cheng <imcheng@chromium.org>
Commit-Queue: Takumi Fujimoto <takumif@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579943}

chrome/browser/ui/views/media_router/cast_dialog_view.cc

@@ -314,8 +314,10 @@ void CastDialogView::RestoreSinkListState() {
 
   views::ScrollBar* scroll_bar =
       const_cast<views::ScrollBar*>(scroll_view_->vertical_scroll_bar());
-  if (scroll_bar)
+  if (scroll_bar) {
     scroll_view_->ScrollToPosition(scroll_bar, scroll_position_);
+    scroll_view_->Layout();
+  }
 }
 
 void CastDialogView::PopulateScrollView(const std::vector<UIMediaSink>& sinks) {