Add additional UMA stats for remembering certificate decisions.

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 9ef66e50e646f39727ae34f685e46621f02157e3..d06d8a7b7d4abf2457b64f2d49a706008cbfaa41 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -9756,6 +9756,16 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="interstitial.ssl.is_expired_and_decision"
+    enum="SSLIsExpiredAndDecision">
+  <owner>jww@chromium.org</owner>
+  <summary>
+    Records when a user decision is made on an overridable SSL interstitial and
+    whether the decision is proceed or not proceed, and whether the user had a
+    previous decision that had expired or not.

[felt, 2014/08/08 00:18:00]

this is rather long and hard to follow

[jww, 2014/08/08 15:55:45]

I tried to simplify it, but I'm not sure if it's still confusing. Please check
out the new summary, and if you have any suggestions, I'm all ears.

+  </summary>
+</histogram>
+
 <histogram name="interstitial.ssl_accept_time" units="milliseconds">
   <obsolete>
     Removed on 8/1/13.
@@ -48225,6 +48235,13 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="9" label="UNKNOWN"/>
 </enum>
 
+<enum name="SSLIsExpiredAndDecision" type="int">
+  <int value="0" label="EXPIRED_AND_PROCEED"/>
+  <int value="1" label="EXPIRED_AND_DO_NOT_PROCEED"/>
+  <int value="2" label="NOT_EXPIRED_AND_PROCEED"/>
+  <int value="3" label="NOT_EXPIRED_AND_DO_NOT_PROCEED"/>
+</enum>
+
 <enum name="SSLNonAttackCauses" type="int">
   <int value="0" label="CLOCK_PAST: System clock set early"/>
   <int value="1" label="CLOCK_FUTURE: System clock set late"/>