Adding DRP specfic UMA for FirstContentfulPaint

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 07be787606d0f1d911f763b55f01147541fb6828..a72cf368f2c848e3f29783b8059f272742b3e612 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -91968,20 +91968,29 @@ To add a new entry, add it with any value and run test to compute valid value.
   <suffix name="Clients.FromGWS"
       label="PageLoadMetrics that are a result of a navigation from a Google
              web search">
     <obsolete>
       Deprecated in favor of Clients.FromGWS2.
     </obsolete>
   </suffix>
   <suffix name="Clients.FromGWS2"
       label="PageLoadMetrics that are a result of a navigation from a Google
              web search"/>
+  <suffix name="Clients.DataReductionProxy"
+      label="PageLoadMetrics that are a result of a navigation through the
+             data reduction proxy."/>
+  <suffix name="Clients.DataReductionProxy.AutoLoFiOn"
+      label="PageLoadMetrics that are a result of a navigation through the
+             data reduction proxy with auto LoFi enabled."/>
+  <suffix name="Clients.DataReductionProxy.AutoLoFiOff"
+      label="PageLoadMetrics that are a result of a navigation through the
+             data reduction proxy with auto LoFi disabled."/>
   <suffix name="Clients.DocWrite.Evaluator"
       label="PageLoadMetrics from a page that could have been evaluated by
              the DocumentWriteEvaluator"/>
   <suffix name="Clients.ServiceWorker"
       label="PageLoadMetrics from a page that is controlled by a Service
              Worker"/>
   <affected-histogram
       name="PageLoad.Timing2.DOMLoadingToDOMContentLoadedEventFired"/>
   <affected-histogram name="PageLoad.Timing2.DOMLoadingToFirstContentfulPaint"/>
   <affected-histogram