Prerender: Remove deprecated prerender experiment 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 4583ac31a33fe39fda310202735974a4c971c1ab..ec6168f3c7c92fe9facb5afb5dad6e0cf2c32271 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -45532,14 +45532,6 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
-<histogram name="Prerender.Sessions" enum="PrerenderMode">
-  <obsolete>
-    deprecated Nov 16 2012
-  </obsolete>
-  <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
-  <summary>Enumeration of how prerender was used per session.</summary>
-</histogram>
-
 <histogram name="Prerender.SessionStorageNamespaceMergeTime" units="ms">
   <obsolete>
     Deprecated Dec 12 2014.
@@ -90020,21 +90012,6 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="19" label="PRERENDER_USED_5"/>
 </enum>
 
-<enum name="PrerenderMode" type="int">

[pasko, 2016/08/24 13:08:29]

We should not remove anything from histograms.xml because we might still want to
look at old data on the dashboard, and the dashboard just uses the latest
histograms.xml.

[mattcary, 2016/08/24 15:49:11]

Done.

-  <obsolete>
-    deprecated Nov 16 2012
-  </obsolete>
-  <int value="0" label="PRERENDER_MODE_DISABLED"/>
-  <int value="1" label="PRERENDER_MODE_ENABLED"/>
-  <int value="2" label="PRERENDER_MODE_EXPERIMENT_CONTROL_GROUP"/>
-  <int value="3" label="PRERENDER_MODE_EXPERIMENT_PRERENDER_GROUP"/>
-  <int value="4" label="PRERENDER_MODE_EXPERIMENT_5MIN_TTL_GROUP"/>
-  <int value="5" label="PRERENDER_MODE_EXPERIMENT_NO_USE_GROUP"/>
-  <int value="6" label="PRERENDER_MODE_EXPERIMENT_MULTI_PRERENDER_GROUP"/>
-  <int value="7" label="PRERENDER_MODE_EXPERIMENT_15MIN_TTL_GROUP"/>
-  <int value="8" label="PRERENDER_MODE_EXPERIMENT_MATCH_COMPLETE_GROUP"/>
-</enum>
-
 <enum name="PrerenderPageviewEvents" type="int">
   <obsolete>
     deprecated Nov 16 2012