Migrate startup URLs pref.

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 880dfb67fecf6c9ff0cd4db96503f4af0cec01ba..ceb1be50fc8add06f10b0b5aa1de0b16931df0cd 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -15336,6 +15336,16 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="Settings.StartupURLsMigration" enum="StartupURLsMigration">
+  <summary>The startup URLs pref migration steps.</summary>
+</histogram>
+
+<histogram name="Settings.StartupURLsResetTime" units="milliseconds">
+  <summary>
+    The time elapsed in miliseconds in between startup URLs pref migration.
+  </summary>
+</histogram>
+
 <histogram name="Settings.TrackedPreferenceChanged" enum="TrackedPreference">
   <summary>
     The id of a tracked preference whose value has been changed since the last
@@ -26656,6 +26666,12 @@ other types of suffix sets.
   <int value="15" label="PROCEED_NEW_SITE"/>
 </enum>
 
+<enum name="StartupURLsMigration" type="int">
+  <int value="0" label="Started"/>
+  <int value="1" label="Deleted"/>
+  <int value="2" label="Reset"/>
+</enum>
+
 <enum name="SuspendStatus" type="int">
   <int value="0" label="Success"/>
   <int value="1" label="Failure"/>