Record scheme of the data reduction proxy server

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 2b159ee38b2703c644a8f7218ec1ed0e4e300e8e..d892507f6e448ad162e1b8d8ca7bc3d47c2f3708 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -8525,6 +8525,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="DataReductionProxy.ProxySchemeUsed"
+    enum="DataReductionProxyProxySchemeUsed">
+  <owner>tbansal@chromium.org</owner>
+  <owner>bengr@chromium.org</owner>
+  <summary>
+    Records the scheme of the data reduction proxy server. Recorded for every
+    request that is fetched successfully through a data reduction proxy server.
+  </summary>
+</histogram>
+
 <histogram name="DataReductionProxy.Quic.OnAlternativeProxyBroken"
     units="count">
   <owner>tbansal@chromium.org</owner>
@@ -76935,6 +76945,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
              *.googlezip.net proxy was cleared"/>
 </enum>
 
+<enum name="DataReductionProxyProxySchemeUsed" type="int">
+  <int value="0" label="Unknown"/>
+  <int value="1" label="HTTP"/>
+  <int value="2" label="HTTPS"/>
+  <int value="3" label="QUIC"/>
+</enum>
+
 <enum name="DataReductionProxyQuicProxyStatus" type="int">
   <int value="0" label="QUIC proxy was available"/>
   <int value="1"