Add histograms for notification icons.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index e07d2185a62c87bcea31a6a70b4f1f495bd0be58..5b43e800a55a3964b0f49067a25d63c96680d933 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -31549,6 +31549,35 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Notifications.Icon.FileSize" units="bytes">
+  <owner>mvanouwerkerk@chromium.org</owner>
+  <summary>The number of bytes loaded for a Web Notification icon.</summary>
+</histogram>
+
+<histogram name="Notifications.Icon.LoadFailTime" units="ms">
+  <owner>mvanouwerkerk@chromium.org</owner>
+  <summary>
+    The number of milliseconds it took to fail loading an icon for a Web
+    Notification.
+  </summary>
+</histogram>
+
+<histogram name="Notifications.Icon.LoadFinishTime" units="ms">
+  <owner>mvanouwerkerk@chromium.org</owner>
+  <summary>
+    The number of milliseconds it took to finish successfully loading an icon
+    for a Web Notification.
+  </summary>
+</histogram>
+
+<histogram name="Notifications.Icon.ScaleDownTime" units="ms">
+  <owner>mvanouwerkerk@chromium.org</owner>
+  <summary>
+    The number of milliseconds it took to scale down an icon for a Web
+    Notification.
+  </summary>
+</histogram>
+
 <histogram name="Notifications.PerNotificationActions"
     enum="NotificationActionType">
   <owner>dewittj@chromium.org</owner>