Add histogram for pages to open enum on session restore.

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 7b4d26dddfcbc1d89717a0e0a2d05291d52a6f73..e009ca9ec35306f5a0348ddffd27242f0c62cb57 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -12821,6 +12821,10 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="Settings.SessionRestoreOnStartup" enum="StartupPagePref">
+  <summary>Records startup page settings when a profile is loaded.</summary>
+</histogram>
+
 <histogram name="Settings.ShowHomeButton" enum="BooleanEnabled">
   <summary>
     Whether or not the Home button is enabled in user preferences when a profile
@@ -21222,6 +21226,16 @@ other types of suffix sets.
   <int value="49323" label="TLS_PSK_DHE_WITH_AES_256_CCM_8"/>
 </enum>
 
+<enum name="StartupPagePref" type="int">
+  <int value="0" label="None"/>
+  <int value="1" label="Open homepage (unused)"/>
+  <int value="2" label="Open new tab page"/>
+  <int value="3" label="Continue from last opened pages"/>
+  <int value="4" label="Open zero URLs"/>
+  <int value="5" label="Open one URL"/>
+  <int value="6" label="Open multiple URLs"/>
+</enum>
+
 <enum name="SuspendStatus" type="int">
   <int value="0" label="Success"/>
   <int value="1" label="Failure"/>