Adding <keygen> Content Setting (UI)

chrome/browser/resources/options/content_settings_exceptions_area.html

 <div id="content-settings-exceptions-area" class="page" hidden>
   <div class="close-button"></div>
   <h1></h1>
   <div class="content-area">
     <div id="exception-column-headers">
       <div id="exception-pattern-column" i18n-content="exceptionPatternHeader">
       </div>
       <div id="exception-behavior-column"
           i18n-content="exceptionBehaviorHeader"
           class="exception-value-column-header">
@@ skipping 25 matching lines @@
       </div>
     </div>
     <div contentType="javascript">
       <list mode="normal"></list>
       <div>
         <span class="otr-explanation" i18n-content="otrExceptionsExplanation">
         </span>
         <list mode="otr"></list>
       </div>
     </div>
+    <div contentType="keygen">

[msramek, 2015/11/05 16:22:31]

I would recommend putting this towards the bottom of the list, as it is probably
not going to be used by a lot of users.

[svaldez, 2015/11/05 16:35:12]

Done.

+      <list mode="normal"></list>
+      <div>
+        <span class="otr-explanation" i18n-content="otrExceptionsExplanation">
+        </span>
+        <list mode="otr"></list>
+      </div>
+    </div>
     <div contentType="plugins">
       <list mode="normal"></list>
       <div>
         <span class="otr-explanation" i18n-content="otrExceptionsExplanation">
         </span>
         <list mode="otr"></list>
       </div>
     </div>
     <div contentType="popups">
       <list mode="normal"></list>
@@ skipping 104 matching lines @@
     </div>
     <div class="action-area-right">
       <div class="button-strip">
         <button id="content-settings-exceptions-overlay-confirm"
             class="default-button" i18n-content="done">
         </button>
       </div>
     </div>
   </div>
 </div>