Add custom interstitial for captive portals.

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 9f0f16be938fb82af21bb52fbf60ef9e2a80baa5..df31138111e68531540d88e27a3736571083b609 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -9059,6 +9059,14 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="interstitial.captive_portal"
+    enum="CaptivePortalBlockingPageEvent">
+  <owner>meacer@chromium.org</owner>
+  <summary>
+    User action when the user is shown a captive portal error page.
+  </summary>
+</histogram>
+
 <histogram name="interstitial.common_name_invalid_time" units="milliseconds">
   <obsolete>
     Removed on 8/1/13.
@@ -33690,6 +33698,12 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="3" label="webgl"/>
 </enum>
 
+<enum name="CaptivePortalBlockingPageEvent" type="int">
+  <int value="0" label="SHOW_ALL"/>
+  <int value="1" label="OPEN_LOGIN_PAGE"/>
+  <int value="2" label="MORE"/>
+</enum>
+
 <enum name="CaptivePortalDetectResult" type="int">
   <int value="0" label="INTERNET_CONNECTED"/>
   <int value="1" label="NO_RESPONSE"/>