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 82c07ac8a1029d00bae937ae6976706685eb7e0d..d22bad345e82ff0ea6bd4fd9d774fec07684f8c0 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -15398,6 +15398,16 @@ 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.

[Alexei Svitkine (slow), 2013/10/15 14:40:55]

Nit: milliseconds (two l's)

Mention that a value of 0 indicates that the last migration time was in the
future (e.g. due to wrong system time).

[robertshield, 2013/10/15 18:00:44]

Done.

+  </summary>
+</histogram>
+
 <histogram name="Settings.TrackedPreferenceChanged" enum="TrackedPreference">
   <summary>
     The id of a tracked preference whose value has been changed since the last
@@ -27029,6 +27039,12 @@ other types of suffix sets.
   <int value="15" label="PROCEED_NEW_SITE"/>
 </enum>
 
+<enum name="StartupURLsMigration" type="int">
+  <int value="0" label="Started"/>

[Alexei Svitkine (slow), 2013/10/15 14:40:55]

Nit: "Started migration" - same for the others below.

[robertshield, 2013/10/15 18:00:44]

Done.

+  <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"/>