Add a histogram for each time the HTTP Bad UI is shown

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 9e8ac8647c0559bc4f45c6f0ffa9cb47e3ae90f7..8c7557c465c138a41e99223e359b33e3ea7e0983 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -56101,6 +56101,17 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Security.HTTPBad.UserWarnedAboutSensitiveInput">

[rkaplow, 2016/10/28 01:07:31]

should have enum="Boolean"

[elawrence, 2016/10/28 01:33:40]

Can I use "BooleanShown" to match what we're really tracking?

+  <owner>elawrence@chromium.org</owner>
+  <owner>estark@chromium.org</owner>
+  <summary>
+    Counts the number of main-frame navigations on which a &quot;Not

[rkaplow, 2016/10/28 01:07:31]

I wouldn't describe this as "counts the number of times" since it is a boolean.
I would describe it given a single instance of an event.

[elawrence, 2016/10/28 01:33:40]

Done.

+    secure" warning was shown in the omnibox due to sensitive form fields
+    appearing on HTTP pages. False values indicate the count of times that only
+    a console warning was shown.
+  </summary>
+</histogram>
+
 <histogram name="Security.PageInfo.Action.HttpsUrl.Dangerous"
     enum="WebsiteSettingsAction">
   <owner>estark@chromium.org</owner>