Fix accessibility issues in message center

- introduce MessageCenterScrollView and use for
MessageCenterView::scroller_. We need this because the |scroller_| is
the one that gets focused when a user invokes Alt+Shift+N.

- remove accessibility bits from MessageCenterView including accessible
data and focusability.

Test: with ChromeVox, press Alt+Shift+N and tab around. Verify that the
scroller gets focused and outputs correctly when first entering message
center and that tabbing never reaches the MessageCenterView, but only
reaches the scroller_. Previously, both were tab stops.

Bug: 
Change-Id: I1c8b06f157bbb4749f61cdd6a4f80c5693d76f48
Reviewed-on: https://chromium-review.googlesource.com/801344
Commit-Queue: David Tseng <dtseng@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521130}

ash/message_center/message_center_view.cc

@@ -108,6 +108,22 @@ class EmptyNotificationView : public views::View {
   DISALLOW_COPY_AND_ASSIGN(EmptyNotificationView);
 };
 
+class MessageCenterScrollView : public views::ScrollView {
+ public:
+  explicit MessageCenterScrollView(MessageCenterView* owner) : owner_(owner) {}
+
+ private:
+  // views::View:
+  void GetAccessibleNodeData(ui::AXNodeData* node_data) override {
+    node_data->role = ui::AX_ROLE_DIALOG;
+    node_data->SetName(owner_->GetButtonBarTitle());
+  }
+
+  MessageCenterView* owner_;
+
+  DISALLOW_COPY_AND_ASSIGN(MessageCenterScrollView);
+};
+
 }  // namespace
 
 // MessageCenterView ///////////////////////////////////////////////////////////
@@ -129,7 +145,7 @@ MessageCenterView::MessageCenterView(
   message_center_->AddObserver(this);
   set_notify_enter_exit_on_child(true);
   SetBackground(views::CreateSolidBackground(kBackgroundColor));
-  SetFocusBehavior(views::View::FocusBehavior::ALWAYS);
+  SetFocusBehavior(views::View::FocusBehavior::NEVER);
 
   button_bar_ = new MessageCenterButtonBar(
       this, message_center, initially_settings_visible, GetButtonBarTitle());
@@ -137,7 +153,7 @@ MessageCenterView::MessageCenterView(
 
   const int button_height = button_bar_->GetPreferredSize().height();
 
-  scroller_ = new views::ScrollView();
+  scroller_ = new MessageCenterScrollView(this);
   scroller_->SetBackgroundColor(kBackgroundColor);
   scroller_->ClipHeightTo(kMinScrollViewHeight, max_height - button_height);
   scroller_->SetVerticalScrollBar(new views::OverlayScrollBar(false));
@@ -266,6 +282,12 @@ void MessageCenterView::SetIsClosing(bool is_closing) {
     message_center_->AddObserver(this);
 }
 
+base::string16 MessageCenterView::GetButtonBarTitle() const {
+  return is_locked_ ?
+      l10n_util::GetStringUTF16(IDS_ASH_MESSAGE_CENTER_FOOTER_LOCKSCREEN) :
+          l10n_util::GetStringUTF16(IDS_ASH_MESSAGE_CENTER_FOOTER_TITLE);
+}
+
 void MessageCenterView::OnDidChangeFocus(views::View* before,
                                          views::View* now) {
   // Update the button visibility when the focus state is changed.
@@ -356,11 +378,6 @@ void MessageCenterView::OnMouseExited(const ui::MouseEvent& event) {
   Update(true /* animate */);
 }
 
-void MessageCenterView::GetAccessibleNodeData(ui::AXNodeData* node_data) {
-  node_data->role = ui::AX_ROLE_DIALOG;
-  node_data->SetName(GetButtonBarTitle());
-}
-
 void MessageCenterView::OnNotificationAdded(const std::string& id) {
   int index = 0;
   const NotificationList::Notifications& notifications =
@@ -543,13 +560,6 @@ void MessageCenterView::AddNotificationAt(const Notification& notification,
   message_list_view_->AddNotificationAt(view, index);
 }
 
-base::string16 MessageCenterView::GetButtonBarTitle() const {
-  if (is_locked_)
-    return l10n_util::GetStringUTF16(IDS_ASH_MESSAGE_CENTER_FOOTER_LOCKSCREEN);
-
-  return l10n_util::GetStringUTF16(IDS_ASH_MESSAGE_CENTER_FOOTER_TITLE);
-}
-
 void MessageCenterView::Update(bool animate) {
   bool no_message_views = (message_list_view_->GetNotificationCount() == 0);
 

ash/message_center/message_center_view.h

@@ -71,6 +71,8 @@ class ASH_EXPORT MessageCenterView
 
   void SetIsClosing(bool is_closing);
 
+  base::string16 GetButtonBarTitle() const;
+
   // Overridden from views::FocusChangeListener
   void OnWillChangeFocus(views::View* before, views::View* now) override {}
   void OnDidChangeFocus(views::View* before, views::View* now) override;
@@ -82,7 +84,7 @@ class ASH_EXPORT MessageCenterView
 
  protected:
   // Potentially sets the reposition target, and then returns whether or not it
-  // was was set.
+  // was set.
   virtual bool SetRepositionTarget();
 
   // Overridden from views::View:
@@ -91,7 +93,6 @@ class ASH_EXPORT MessageCenterView
   int GetHeightForWidth(int width) const override;
   bool OnMouseWheel(const ui::MouseWheelEvent& event) override;
   void OnMouseExited(const ui::MouseEvent& event) override;
-  void GetAccessibleNodeData(ui::AXNodeData* node_data) override;
 
   // Overridden from MessageCenterObserver:
   void OnNotificationAdded(const std::string& id) override;
@@ -137,7 +138,6 @@ class ASH_EXPORT MessageCenterView
 
   void AddNotificationAt(const message_center::Notification& notification,
                          int index);
-  base::string16 GetButtonBarTitle() const;
   void Update(bool animate);
   void SetVisibilityMode(Mode mode, bool animate);
   void UpdateButtonBarStatus();