NTP: add histogram to track New Tab page URL status.

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 d1a1a1030dc9e6a44c3401bee9e6867d3cf3900a..484dae73ef6601e913231063179275ff5fca4b7d 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -6045,6 +6045,10 @@ other types of suffix sets.
 
 <histogram name="InstantExtended.FallbackToLocalOverlay"
     enum="InstantExtended_FallbackCause">
+  <obsolete>
+    Depcreated as of 10/2013. No longer relevant since the HTML overlay was
+    abandoned.
+  </obsolete>
   <summary>
     Records the cause for falling back to a local overlay at the time of
     fallback.
@@ -12111,6 +12115,12 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="NewTabPage.URLState" enum="NewTabURLState">
+  <summary>
+    Records the status of the New Tab page URL when an NTP is opened.
+  </summary>
+</histogram>
+
 <histogram name="NewTabPage.VisibleScreenshots">
   <summary>
     The number of screenshots that were cached for the visible suggestions on
@@ -28286,6 +28296,16 @@ other types of suffix sets.
   <int value="4" label="User dismissed the promo"/>
 </enum>
 
+<enum name="NewTabURLState" type="int">
+  <int value="0" label="Valid URL that was used"/>

[Alexei Svitkine (slow), 2014/02/03 18:08:38]

Nit: "Valid URL was used"

[samarth, 2014/02/03 18:33:31]

Done.

+  <int value="1" label="Corrupt state"/>
+  <int value="2" label="Incognito window"/>
+  <int value="3" label="No URL for default provider"/>
+  <int value="4" label="Insecure URL"/>
+  <int value="5" label="Suggest is disabled"/>
+  <int value="6" label="URL blocked for supervised user"/>
+</enum>
+
 <enum name="NotificationActionType" type="int">
   <int value="0" label="Unknown"/>
   <int value="1" label="Notification added"/>