Record DRP histogram on how long back savings were cleared

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 f01549cc4f4725adacd5e1d3b19e9c97220cec33..175d0766419e6216015a165dcf0076688eaeb877 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -8694,6 +8694,19 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram
+    name="DataReductionProxy.DaysSinceSavingsCleared.NegativeSystemClock"
+    units="days">
+  <owner>tbansal@chromium.org</owner>
+  <owner>bengr@chromium.org</owner>
+  <summary>
+    Records the number of days since the data reduction savings were cleared
+    because the system clock moved back by more than 1 day. Recorded at Chrome
+    startup if data reduction proxy is enabled, and if the data reduction proxy
+    savings were cleared in some previous Chrome session.
+  </summary>
+</histogram>
+
 <histogram name="DataReductionProxy.EnabledState"
     enum="DataReductionProxyEnabledState">
   <owner>bengr@chromium.org</owner>
@@ -9043,6 +9056,17 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="DataReductionProxy.SavingsCleared.NegativeSystemClock"
+    enum="BooleanCleared">
+  <owner>tbansal@chromium.org</owner>
+  <owner>bengr@chromium.org</owner>
+  <summary>
+    Records if the data reduction savings were cleared because the system clock
+    moved back by more than 1 day. Recorded at Chrome startup if the data
+    reduction proxy is enabled.
+  </summary>
+</histogram>
+
 <histogram name="DataReductionProxy.SecureProxyCheck.Latency" units="ms">
   <owner>bengr@chromium.org</owner>
   <summary>
@@ -77193,6 +77217,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="1" label="Checked"/>
 </enum>
 
+<enum name="BooleanCleared" type="int">
+  <int value="0" label="Not cleared"/>
+  <int value="1" label="Cleared"/>
+</enum>
+
 <enum name="BooleanClicked" type="int">
   <int value="0" label="Not Clicked"/>
   <int value="1" label="Clicked"/>