Record download target connection security state

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 b7beca498562ee3eb52fdfbf68bad3141325576b..1e78bd2a2607d4fd8ba7ac065dc8afcae7138ea0 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -11499,6 +11499,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Download.TargetConnectionSecurity"
+    enum="DownloadConnectionSecurity">
+  <owner>jialiul@chromium.org</owner>
+  <summary>
+    The connection security state of a download, indicating whether its final
+    resolved url and the redirects before final url are secure.
+  </summary>
+</histogram>
+
 <histogram name="Download.Time" units="ms">
   <owner>asanka@chromium.org</owner>
   <summary>Time between the start of a download and its completion.</summary>
@@ -75557,6 +75566,19 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="3" label="Touch"/>
 </enum>
 
+<enum name="DownloadConnectionSecurity" type="int">
+  <int value="0"
+      label="Final download url and the redirects before it all use https"/>
+  <int value="1" label="Final download url uses http, redirects all use https"/>
+  <int value="2"
+      label="Final download url uses https, but at least one redirect uses
+             http"/>
+  <int value="3"
+      label="Final download url uses http, and at least one redirect uses
+             http"/>
+  <int value="4" label="Final download url uses scheme other than http/https"/>
+</enum>
+
 <enum name="DownloadContentDisposition" type="int">
   <int value="0" label="Content-Disposition header present"/>
   <int value="1" label="Valid"/>