Distinguishes "nothing new" and "should be empty" in display notifications.

Sometimes OnDisplayConfigurationChanged() can be called twice or
even more, and in that case the notification will be cleared. This
is a side effect of closing stale notifications. We should distinguish
"nothing new happened actually" from "the notification should be
cleared", both has empty |message|.

BUG=260977
R=oshima@chromium.org
TEST=the new test case covers

Review URL: https://chromiumcodereview.appspot.com/19502002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@212468 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 7 insertions, 5 deletions

diff --git a/ash/system/chromeos/tray_display.h b/ash/system/chromeos/tray_display.h
index 7ede247..7adbd31 100644
--- a/ash/system/chromeos/tray_display.h
+++ b/ash/system/chromeos/tray_display.h
@@ -29,22 +29,24 @@ class ASH_EXPORT TrayDisplay : public SystemTrayItem,
   explicit TrayDisplay(SystemTray* system_tray);
   virtual ~TrayDisplay();
 
+  // Overridden from DisplayControllerObserver:
+  virtual void OnDisplayConfigurationChanged() OVERRIDE;
+
  private:
   friend class TrayDisplayTest;
 
   typedef std::map<int64, DisplayInfo> DisplayInfoMap;
 
   // Checks the current display settings and determine what message should be
-  // shown for notification.
-  base::string16 GetDisplayMessageForNotification();
+  // shown for notification. Returns true if there's a meaningful change. Note
+  // that it's possible to return true and set |message| to empty, which means
+  // the notification should be removed.
+  bool GetDisplayMessageForNotification(base::string16* message);
 
   // Overridden from SystemTrayItem.
   virtual views::View* CreateDefaultView(user::LoginStatus status) OVERRIDE;
   virtual void DestroyDefaultView() OVERRIDE;
 
-  // Overridden from DisplayControllerObserver:
-  virtual void OnDisplayConfigurationChanged() OVERRIDE;
-
   // Test accessors.
   base::string16 GetDefaultViewMessage();
   base::string16 GetNotificationMessage();