Add a QUIC proxy server to the list of QUIC servers supported at start up

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 f88bbca1cdc651b8c4c1dc305195f6e397ead7fc..3d1b7232c1bb43f4e62960f3ec41d1616697494d 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -8656,6 +8656,17 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="DataReductionProxy.Quic.DefaultAlternativeProxy"
+    enum="DataReductionProxyQuicDefaultAlternativeProxy">
+  <owner>tbansal@chromium.org</owner>
+  <owner>bengr@chromium.org</owner>
+  <summary>
+    Status of the availability of valid alternative data reduction proxy
+    servers. This metric is recorded only when data reduction proxy delegate is
+    queried for the value of the supported alternative proxy server.
+  </summary>
+</histogram>
+
 <histogram name="DataReductionProxy.Quic.OnAlternativeProxyBroken"
     units="count">
   <owner>tbansal@chromium.org</owner>
@@ -77972,6 +77983,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="3" label="QUIC"/>
 </enum>
 
+<enum name="DataReductionProxyQuicDefaultAlternativeProxy" type="int">
+  <int value="0" label="QUIC proxy was available"/>
+  <int value="1" label="QUIC proxy was marked as broken"/>
+  <int value="2"
+      label="No supportable QUIC proxy was available in the list of data
+             reduction proxies"/>
+</enum>
+
 <enum name="DataReductionProxyQuicProxyStatus" type="int">
   <int value="0" label="QUIC proxy was available"/>
   <int value="1"