MD Settings: Add placeholder text when adding/editing a content exception.

chrome/app/settings_strings.grdp

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Settings-specific strings (included from generated_resources.grd). -->
 <grit-part>
   <!-- Main Page -->
   <if expr="chromeos">
     <message name="IDS_SETTINGS_SECONDARY_USER_BANNER" desc="Banner displayed in settings page when the user is secondary in a multi-profile session.">
       Some settings belonging to <ph name="PRIMARY_EMAIL">$1<ex>john@google.com</ex></ph> are being shared with you. These settings only affect your account when using multiple sign-in.
     </message>
   </if>
 
@@ skipping 2011 matching lines @@
   <message name="IDS_SETTINGS_SITE_SETTINGS_NO_ZOOMED_SITES" desc="A label explaining that no sites have a configured zoom in/out value.">
     No sites have been zoomed in or out.
   </message>
   <message name="IDS_SETTINGS_SITE_DETAILS" desc="A title for the site settings details subpage.">
     Site details
   </message>
   <message name="IDS_SETTINGS_SITE_NO_SITES_ADDED" desc="Explenation for not showing a list of site exceptions">
     No sites added
   </message>
 
+  <message name="IDS_SETTINGS_ADD_SITE_EXCEPTION_PLACEHOLDER" desc="Placeholder text shown before the user starts typing a new content settings exception for a site." >
+    [*.]example.com
+  </message>
   <message name="IDS_SETTINGS_ADD_SITE_LINK" desc="Link text to show (to open the Add Site dialog)">
     Add site exception
   </message>
   <message name="IDS_SETTINGS_ADD_SITE_TITLE" desc="Title for the Add Site dialog">
     Add an exception for a site
   </message>
   <message name="IDS_SETTINGS_EDIT_SITE_TITLE" desc="Title for the Edit Site dialog">
     Edit exception
   </message>
   <message name="IDS_SETTINGS_ADD_SITE" desc="The label for the input box for adding a site">
@@ skipping 856 matching lines @@
       System
     </message>
     <message name="IDS_SETTINGS_SYSTEM_HARDWARE_ACCELERATION_LABEL" desc="Label for the checkbox that forces Chrome to render via hardware acceleration (GPU) when available.">
       Use hardware acceleration when available
     </message>
     <message name="IDS_SETTINGS_SYSTEM_PROXY_SETTINGS_BUTTON" desc="Text for the button that changes a user's network proxy settings.">
       Change proxy settings
     </message>
   </if>
 </grit-part>