Obsolete unused PLT 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 25bab1dec629acb8992e973b0322a630bc709dac..7b5fb89a8e3a26f004d44d243e3fae2bf4928cb2 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -41286,6 +41286,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="PLT.BeginToFinish_ContentPrefetcher" units="ms">
+  <obsolete>
+    No longer needed.
+  </obsolete>
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>
     PLT.BeginToFinish, but for pages which contained prefetch links.
@@ -41293,6 +41296,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="PLT.BeginToFinish_ContentPrefetcherReferrer" units="ms">
+  <obsolete>
+    No longer needed.
+  </obsolete>
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>
     PLT.BeginToFinish, but for pages which were referred to by pages which
@@ -41321,6 +41327,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 
 <histogram name="PLT.BeginToFinish_LinkLoadNormal_ExtensionWebRequest"
     units="ms">
+  <obsolete>
+    No longer needed.
+  </obsolete>
   <owner>vabr@chromium.org</owner>
   <summary>
     The PLT.BeginToFinish histogram for pages loaded by following a link, after
@@ -41380,6 +41389,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 
 <histogram name="PLT.BeginToFinish_LinkLoadReload_ExtensionWebRequest"
     units="ms">
+  <obsolete>
+    No longer needed.
+  </obsolete>
   <owner>vabr@chromium.org</owner>
   <summary>
     The PLT.BeginToFinish histogram for pages reloaded by JavaScript or by
@@ -41439,6 +41451,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 
 <histogram name="PLT.BeginToFinish_LinkLoadStaleOk_ExtensionWebRequest"
     units="ms">
+  <obsolete>
+    No longer needed.
+  </obsolete>
   <owner>vabr@chromium.org</owner>
   <summary>
     The PLT.BeginToFinish histogram for pages loads initiated by back/forward
@@ -41494,6 +41509,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="PLT.BeginToFinish_NormalLoad_ExtensionWebRequest" units="ms">
+  <obsolete>
+    No longer needed.
+  </obsolete>
   <owner>vabr@chromium.org</owner>
   <summary>
     The PLT.BeginToFinish histogram for pages loaded by entering a URL or a
@@ -41529,6 +41547,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="PLT.BeginToFinish_SpdyProxy" units="ms">
+  <obsolete>
+    Use PLT.PT_BeginToFinish_DataReductionProxy instead.
+  </obsolete>
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>PLT.BeginToFinish, but for pages fetched over a SPDY proxy.</summary>
 </histogram>
@@ -41550,6 +41571,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="PLT.BeginToFinishDoc_ContentPrefetcher" units="ms">
+  <obsolete>
+    No longer needed.
+  </obsolete>
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>
     PLT.BeginToFinishDoc, but for pages which contained prefetch links.
@@ -41557,6 +41581,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="PLT.BeginToFinishDoc_ContentPrefetcherReferrer" units="ms">
+  <obsolete>
+    No longer needed.
+  </obsolete>
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>
     PLT.BeginToFinishDoc, but for pages which were referred to by pages which
@@ -41565,6 +41592,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="PLT.BeginToFinishDoc_SpdyProxy" units="ms">
+  <obsolete>
+    Use PLT.PT_BeginToFinishDoc_DataReductionProxy instead.
+  </obsolete>
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>
     PLT.BeginToFinshDoc, but for pages fetched over a SPDY proxy.