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 f47f6a8feb182b10fc6e905ee83ae5c6efb3dd5c..f19a1b3c66400e1cbc3dc2d7079979fce7ffa282 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -84333,20 +84333,21 @@ To add a new entry, add it with any value and run test to compute valid value.
   <affected-histogram name="Tabs.StateTransfer.Target"/>
   <affected-histogram name="Tabs.StateTransfer.Time"/>
 </histogram_suffixes>
 
 <histogram_suffixes name="DataReductionProxy">
   <suffix name="DataReductionProxy"
       label="Only page loads through the data reduction proxy are considered."/>
   <suffix name="HTTPS_DataReductionProxy"
       label="Only page loads through the data reduction proxy through an HTTP
              tunnel for HTTPS origins are considered."/>
+  <affected-histogram name="PageLoad.Timing2.NavigationToFirstContentfulPaint"/>
   <affected-histogram name="PLT.NT_Connect"/>
   <affected-histogram name="PLT.NT_DelayBeforeConnect"/>
   <affected-histogram name="PLT.NT_DelayBeforeDomainLookup"/>
   <affected-histogram name="PLT.NT_DelayBeforeDomLoading"/>
   <affected-histogram name="PLT.NT_DelayBeforeFetch"/>
   <affected-histogram name="PLT.NT_DelayBeforeFetchRedirect"/>
   <affected-histogram name="PLT.NT_DelayBeforeLoadEvent"/>
   <affected-histogram name="PLT.NT_DelayBeforeRequest"/>
   <affected-histogram name="PLT.NT_DomainLookup"/>
   <affected-histogram name="PLT.NT_DomContentLoaded"/>
@@ -84416,20 +84417,21 @@ To add a new entry, add it with any value and run test to compute valid value.
              enabled are considered."/>
   <suffix name="DataReductionProxy_AutoLoFiOff"
       label="Only page loads through the data reduction proxy with auto LoFi
              disabled are considered."/>
   <suffix name="HTTPS_DataReductionProxy_AutoLoFiOn"
       label="Only page loads through the data reduction proxy through an HTTP
              tunnel for HTTPS origins with auto LoFi enabled are considered."/>
   <suffix name="HTTPS_DataReductionProxy_AutoLoFiOff"
       label="Only page loads through the data reduction proxy through an HTTP
              tunnel for HTTPS origins with auto LoFi disabled are considered."/>
+  <affected-histogram name="PageLoad.Timing2.NavigationToFirstContentfulPaint"/>
   <affected-histogram name="PLT.BeginToFirstPaint"/>
   <affected-histogram name="PLT.PT_BeginToFinish"/>
   <affected-histogram name="PLT.PT_CommitToFinish"/>
   <affected-histogram name="PLT.PT_RequestToDomContentLoaded"/>
   <affected-histogram name="PLT.PT_RequestToFinish"/>
   <affected-histogram name="PLT.PT_StartToFinish"/>
 </histogram_suffixes>
 
 <histogram_suffixes name="DataReductionProxy_TamperingFingerprints"
     separator="_">