Add security feature to ProvisionalSavePassword

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 0f2cf42fff30c20b3ce732c7a31f96ab04774816..196f67b8deadfaf7f49a5660f3f151c5b4bd1127 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -44532,6 +44532,22 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram
+    name="PasswordManager.ShouldBlockPasswordForSameOriginButDifferentScheme"
+    enum="BooleanBlocked">
+  <owner>jdoerrie@chromium.org</owner>
+  <summary>
+    This metric is recorded every time Chrome detects a password form
+    submission. The credential might be proposed to be saved, or it might be
+    blocked. It is blocked if the previously detected password form submission
+    was successful, and the current submission is from a URL with the same
+    origin, but a different and insecure scheme. That is, if the previously
+    provisionally saved credential is for https://example.com, a new credential
+    for http://example.com would be blocked. More details can be found in the
+    doc associated with http://crbug.com/571580.
+  </summary>
+</histogram>
+
 <histogram name="PasswordManager.ShouldShowAutoSignInFirstRunExperience"
     enum="BooleanPending">
   <owner>vasilii@chromium.org</owner>