guess OS version on checkup page

www/checkup/app-checkup.less

@@ -88,11 +88,10 @@ html, body {
     .cp-notice-browser, .cp-notice-details, .cp-notice-other {
         font-size: 70%;
     }
-
+    .underline { text-decoration: underline; }
     .cp-app-checkup-version, .cp-app-checkup-browser {
-        text-decoration: underline;
+        .underline;
     }
-
     iframe {
         display: none;
     }

www/checkup/checkup-tools.js

@@ -14,6 +14,25 @@ define([
         return false;
     };
 
+    var OS_HINTS = {
+        "Win": "Windows",
+        "Mac": "MacOS",
+        "X11": "UNIX",
+        "Linux": "Linux",
+    };
+
+    Tools.guessOS = function () {
+        var result = "UNKNOWN";
+        if (!window.navigator || !window.navigator.appVersion) { return result; }
+        result = window.navigator.appVersion;
+        console.log(result);
+        Object.keys(OS_HINTS).some(function (key) {
+            if (result.indexOf(key) === -1) { return; }
+            result = OS_HINTS[key]; // else
+            return true;
+        });
+        return result;
+    };
 
     Tools.isSafari = function () {
         return navigator.vendor.match(/apple/i);

www/checkup/main.js

@@ -932,7 +932,9 @@ define([
         return h('p.cp-notice-browser', [
             "You appear to be using a ",
             h('span.cp-app-checkup-browser', name),
-            ' browser to view this page.',
+            ' browser on ',
+            h('span.underline', Tools.guessOS()),
+            ' to view this page.',
         ]);
     };