Remove status icon if there are no more notifications.

This will match the behavior on ChromeOS and ensure that users without
notifications will not be annoyed by the Chrome notifications center
icon in the status tray.

BUG=401215

Review URL: https://codereview.chromium.org/459123002

Cr-Commit-Position: refs/heads/master@{#289128}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289128 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/ui/views/message_center/web_notification_tray.cc

@@ -276,6 +276,11 @@ void WebNotificationTray::UpdateStatusIcon() {
     tool_tip = l10n_util::GetStringUTF16(IDS_MESSAGE_CENTER_TOOLTIP);
   }
 
+  if (message_center()->GetVisibleNotifications().empty()) {
+    DestroyStatusIcon();
+    return;
+  }
+
   gfx::ImageSkia* icon_image = GetIcon(
       unread_notifications,
       message_center()->IsQuietMode());

chrome/browser/ui/views/message_center/web_notification_tray_browsertest.cc

@@ -249,6 +249,6 @@ IN_PROC_BROWSER_TEST_F(WebNotificationTrayTest, MAYBE_StatusIconBehavior) {
   EXPECT_TRUE(tray->status_icon_ != NULL);
   RemoveNotification("test_id");
   base::RunLoop().RunUntilIdle();
-  EXPECT_TRUE(tray->status_icon_ != NULL);
+  EXPECT_TRUE(tray->status_icon_ == NULL);
 }
 }  // namespace message_center