Support tooltip for HoverHighlightView

ash/system/tray/hover_highlight_view.h

Index: ash/system/tray/hover_highlight_view.h
diff --git a/ash/system/tray/hover_highlight_view.h b/ash/system/tray/hover_highlight_view.h
index 6b9d1a22a42dada37b43bc1e360a19c348de0b48..40819bd26b1d239e08a9e24f5ba925b0be7b9ed5 100644
--- a/ash/system/tray/hover_highlight_view.h
+++ b/ash/system/tray/hover_highlight_view.h
@@ -26,6 +26,10 @@ class HoverHighlightView : public ActionableView {
   explicit HoverHighlightView(ViewClickListener* listener);
   ~HoverHighlightView() override;
 
+  // views::View
+  bool GetTooltipText(const gfx::Point& p,
+                      base::string16* tooltip) const override;
+
   // Convenience function for adding an icon and a label. This also sets the
   // accessible name.
   void AddIconAndLabel(const gfx::ImageSkia& image,
@@ -66,6 +70,8 @@ class HoverHighlightView : public ActionableView {
 
   bool hover() const { return hover_; }
 
+  void set_tooltip(const base::string16& tooltip) { tooltip_ = tooltip; }
+
  protected:
   // Overridden from views::View.
   void GetAccessibleState(ui::AXViewState* state) override;
@@ -103,6 +109,7 @@ class HoverHighlightView : public ActionableView {
   bool expandable_;
   bool checkable_;
   bool checked_;
+  base::string16 tooltip_;
 
   DISALLOW_COPY_AND_ASSIGN(HoverHighlightView);
 };