Add a mechanism for collecting Rappor samples on a daily interval.

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 ce6325a46fa61b12806f60dc300e2f5b404b4a8b..5a9d5f0bcd66108811ddb23382ba0262c0b59a0f 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -25621,6 +25621,11 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Rappor.DailyEvent.IntervalType" enum="DailyEventIntervalType">
+  <owner>holte@chromium.org</owner>
+  <summary>Counts how often daily interval events were fired.</summary>
+</histogram>
+
 <histogram name="Rappor.DiscardReason" enum="RapporDiscardReason">
   <owner>holte@chromium.org</owner>
   <summary>
@@ -38461,6 +38466,12 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="8" label="PlayMusic"/>
 </enum>
 
+<enum name="DailyEventIntervalType" type="int">
+  <int value="0" label="First Run"/>
+  <int value="1" label="Day Elapsed"/>
+  <int value="2" label="Clock Changed"/>
+</enum>
+
 <enum name="DataChannelCounters" type="int">
   <int value="0" label="Channel created."/>
   <int value="1" label="Channel reached Open state."/>