Separate page load metrics for backgrounded pages

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 741dded356f3f49f567de14b1789ca972b356639..ac9986057fd12a35a14560ec420279edf33638c6 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -29651,6 +29651,36 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="PageLoad.Timing.BG.NavigationToDOMContentLoadedEventFired"
+    units="milliseconds">
+  <owner>bmcquade@chromium.org</owner>
+  <summary>
+    Measures the time from navigation timing's navigation start to the time the
+    DOMContentLoaded event is fired, for main frame documents that were
+    backgrounded at some point during the page load.
+  </summary>
+</histogram>
+
+<histogram name="PageLoad.Timing.BG.NavigationToFirstLayout"
+    units="milliseconds">
+  <owner>bmcquade@chromium.org</owner>
+  <summary>
+    Measures the time from navigation timing's navigation start to the time the
+    first layout is performed, for main frame documents that were backgrounded
+    at some point during the page load.
+  </summary>
+</histogram>
+
+<histogram name="PageLoad.Timing.BG.NavigationToLoadEventFired"
+    units="milliseconds">
+  <owner>bmcquade@chromium.org</owner>
+  <summary>
+    Measures the time from navigation timing's navigation start to the time the
+    load event is fired, for main frame documents that were backgrounded at some
+    point during the page load.
+  </summary>
+</histogram>
+
 <histogram name="PageLoad.Timing.NavigationToDOMContentLoadedEventFired"
     units="milliseconds">
   <owner>bmcquade@chromium.org</owner>