Deprecate PageLoad.Timing2.NavigationToFirstBackground histograms.

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 9d00901a8d18cb0f51b705b2daf771e47e753501..38cd39136bb41e0d698d42ef6ba68b2de9232d31 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -40828,6 +40828,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="PageLoad.Timing2.NavigationToFirstBackground" units="ms">
+  <obsolete>
+    deprecated in favor of PageLoad.AbortTiming.Background.*
+  </obsolete>
   <owner>bmcquade@chromium.org</owner>
   <owner>csharrison@chromium.org</owner>
   <summary>
@@ -108000,7 +108003,11 @@ value.
   <affected-histogram name="PageLoad.AbortTiming.Reload"/>
   <affected-histogram name="PageLoad.AbortTiming.Stop"/>
   <affected-histogram name="PageLoad.AbortTiming.UnknownNavigation"/>
-  <affected-histogram name="PageLoad.Timing2.NavigationToFirstBackground"/>
+  <affected-histogram name="PageLoad.Timing2.NavigationToFirstBackground">
+    <obsolete>
+      deprecated in favor of PageLoad.AbortTiming.Background.*
+    </obsolete>
+  </affected-histogram>
 </histogram_suffixes>
 
 <histogram_suffixes name="PageLoadMetricsCacheInfo" separator=".">