Add a "session only" policy to the content settings.

chrome/app/generated_resources.grd

 <?xml version="1.0" encoding="UTF-8"?>
 
 <!-- This file contains definitions of resources that will be translated for
 each locale. -->
 
 <grit base_dir="." latest_public_release="0" current_release="1"
       source_lang_id="en" enc_check="möl">
   <outputs>
     <output filename="grit/generated_resources.h" type="rc_header">
       <emit emit_type='prepend'></emit>
@@ skipping 4436 matching lines @@
       </message>
       <message name="IDS_EXCEPTIONS_REMOVEALL_BUTTON" desc="A button in exception dialogs for removing all exception rules.">
         Remove All
       </message>
       <message name="IDS_EXCEPTIONS_ALLOW_BUTTON" desc="A label to display in the exception page's action column when a site's content setting is allowed for a given domain">
         Allow
       </message>
       <message name="IDS_EXCEPTIONS_ASK_BUTTON" desc="A label to display in the exception page's action column when a site's content setting is set to promt for a given domain.">
         Ask
       </message>
+      <message name="IDS_EXCEPTIONS_SESSION_ONLY_BUTTON" desc="A label to display in the exception page's action column when a site's content setting is allow but only for the duration of the session for a given domain.">
+        Session only
+      </message>
       <message name="IDS_EXCEPTIONS_BLOCK_BUTTON" desc="A label to display in the exception page's action column when a site's content setting is blocked for a given domain.">
         Block
       </message>
       <message name="IDS_EXCEPTIONS_NOT_SET_BUTTON" desc="A label to display in the exception page's action column when a site's content setting has not yet been set for a given domain.">
         Not set
       </message>
       <message name="IDS_EXCEPTIONS_SAMPLE_HOST" desc="Exceptions page view's host entry field's watermark - example host name. Users will see this text before they start typing host name in the field.">
         example.com
       </message>
       <message name="IDS_EXCEPTIONS_SAMPLE_PATTERN" desc="Exceptions page view's pattern entry field's watermark - example pattern. Users will see this text before they start typing pattern in the field.">
@@ skipping 4041 matching lines @@
 
     </messages>
 
     <structures first_id="50000" fallback_to_english="true">
       <structure name="IDD_CHROME_FRAME_FIND_DIALOG" file="cf_resources.rc" type="dialog" >
       </structure>
     </structures>
 
   </release>
 </grit>