Ash Tray: Fix notification list scrolling after toggling check box.

The relayout after toggling a checkbox resets the scroll poition, causing a
jarring scroll to start of the list. The fix is to retain the original scroll
position during the layout.

BUG=1000599

Change-Id: I9102c924ac9526ed604124d99677506bca76469f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1815537Reviewed-by: Ahmed Mehfooz <amehfooz@chromium.org>
Commit-Queue: Tim Song <tengs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#698635}

ash/system/message_center/notifier_settings_view.cc

@@ -419,6 +419,7 @@ NotifierSettingsView::NotifierSettingsView()
       quiet_mode_toggle_(nullptr),
       header_view_(nullptr),
       top_label_(nullptr),
+      scroll_bar_(nullptr),
       scroller_(nullptr),
       no_notifiers_view_(nullptr) {
   SetFocusBehavior(FocusBehavior::ACCESSIBLE_ONLY);
@@ -486,10 +487,11 @@ NotifierSettingsView::NotifierSettingsView()
 
   header_view_ = AddChildView(std::move(header_view));
 
+  scroll_bar_ = new views::OverlayScrollBar(/*horizontal=*/false);
+
   auto scroller = std::make_unique<views::ScrollView>();
   scroller->SetBackgroundColor(SK_ColorTRANSPARENT);
-  scroller->SetVerticalScrollBar(new views::OverlayScrollBar(false));
-  scroller->SetHorizontalScrollBar(new views::OverlayScrollBar(true));
+  scroller->SetVerticalScrollBar(scroll_bar_);
   scroller->SetDrawOverflowIndicator(false);
   scroller_ = AddChildView(std::move(scroller));
 
@@ -577,6 +579,7 @@ void NotifierSettingsView::OnNotifierIconUpdated(const NotifierId& notifier_id,
 }
 
 void NotifierSettingsView::Layout() {
+  int original_scroll_position = scroller_->GetVisibleRect().y();
   int header_height = header_view_->GetHeightForWidth(width());
   header_view_->SetBounds(0, 0, width(), header_height);
 
@@ -591,6 +594,9 @@ void NotifierSettingsView::Layout() {
   scroller_->SetBounds(0, header_height, width(), height() - header_height);
   no_notifiers_view_->SetBounds(0, header_height, width(),
                                 height() - header_height);
+
+  // The scroll position may have changed after the layout.
+  scroller_->ScrollToPosition(scroll_bar_, original_scroll_position);
 }
 
 gfx::Size NotifierSettingsView::GetMinimumSize() const {

ash/system/message_center/notifier_settings_view.h

@@ -20,6 +20,7 @@
 
 namespace views {
 class Label;
+class ScrollBar;
 class ToggleButton;
 }  // namespace views
 
@@ -99,6 +100,7 @@ class ASH_EXPORT NotifierSettingsView : public views::View,
   views::ToggleButton* quiet_mode_toggle_;
   views::View* header_view_;
   views::Label* top_label_;
+  views::ScrollBar* scroll_bar_;
   views::ScrollView* scroller_;
   views::View* no_notifiers_view_;
   std::set<NotifierButton*> buttons_;