Add percentage of progress in notification header.

ui/message_center/views/notification_header_view.h

Index: ui/message_center/views/notification_header_view.h
diff --git a/ui/message_center/views/notification_header_view.h b/ui/message_center/views/notification_header_view.h
index b5fbbc0aa3f3f142394766ade6e3d18d8236918c..bc66ac72d5d5a4ba3e171daf1291f56f7cefdf72 100644
--- a/ui/message_center/views/notification_header_view.h
+++ b/ui/message_center/views/notification_header_view.h
@@ -22,6 +22,7 @@ class NotificationHeaderView : public views::CustomButton {
   NotificationHeaderView(views::ButtonListener* listener);
   void SetAppIcon(const gfx::ImageSkia& img);
   void SetAppName(const base::string16& name);
+  void SetSummaryText(const base::string16& summary_text);

[fukino, 2017/06/22 08:57:43]

optional nit: Instead of having a direct setter for the string, could you add
SetProgress (and SetTimestamp for other notification types) and leave the
responsibility of visual representation to NotificationHeaderView class?

[tetsui, 2017/06/23 02:33:04]

Done.

   void SetExpandButtonEnabled(bool enabled);
   void SetExpanded(bool expanded);
   void SetSettingsButtonEnabled(bool enabled);
@@ -40,6 +41,8 @@ class NotificationHeaderView : public views::CustomButton {
   void UpdateControlButtonsVisibility();
 
   views::Label* app_name_view_ = nullptr;
+  views::Label* summary_text_divider_ = nullptr;
+  views::Label* summary_text_view_ = nullptr;
   views::ImageView* app_icon_view_ = nullptr;
   views::ImageButton* expand_button_ = nullptr;
   PaddedButton* settings_button_ = nullptr;