Fix broken clockstate.network2 histogram and add unit test

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 92ebc71491db905630b318c664a0698750d7f062..e178a92716024cad06f5e395d13342608b2723ff 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -21412,6 +21412,21 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 
 <histogram name="interstitial.ssl.clockstate.network2"
     enum="NetworkClockStates">
+  <obsolete>
+    Deprecated October 2016. Due to a bug, data in this histogram is mislabelled
+    and should be disregarded. Replaced with
+    interstitial.ssl.clockstate.network3.
+  </obsolete>
+  <owner>estark@chromium.org</owner>
+  <owner>mab@chromium.org</owner>
+  <summary>
+    State of the system clock, relative to network time, when an SSL
+    CERT_INVALID_DATE error is seen.
+  </summary>
+</histogram>
+
+<histogram name="interstitial.ssl.clockstate.network3"
+    enum="NetworkClockStates">
   <owner>estark@chromium.org</owner>
   <owner>mab@chromium.org</owner>
   <summary>