Document the activeTab extension permission.

chrome/common/extensions/docs/templates/articles/permission_warnings.html

 <h1>Permission Warnings</h1>
 
 
 <!--
 NOTE: When this doc is updated, the online help should also be updated:
 http://www.google.com/support/chrome_webstore/bin/answer.py?hl=en&answer=186213
 
 We should periodically look at
 http://src.chromium.org/viewvc/chrome/trunk/src/chrome/app/generated_resources.grd?view=markup
 to make sure that we're covering all messages. Search for
@@ skipping 247 matching lines @@
 
     <p>
       Any of the following URLs match all hosts:
     </p>
     <ul>
       <li> <code>http://*/*</code> </li>
       <li> <code>https://*/*</code> </li>
       <li> <code>*://*/*</code> </li>
       <li> <code>&lt;all_urls&gt;</code> </li>
     </ul>
+    <strong>Note that you may be able to avoid declaring all host permissions using the <code><a href="activeTab.html">activeTab</a></code> permission.</strong>
   </td>
 </tr>
 <tr>
   <td style="font-weight:bold">
     <!-- IDS_EXTENSION_PROMPT_WARNING_?_HOST -->
     <!-- IDS_EXTENSION_PROMPT_WARNING_4_OR_MORE_HOSTS -->
     Access your data on <em>{list of websites}</em>
   </td>
   <td>
     A match pattern in the "permissions" field
@@ skipping 114 matching lines @@
 </p>
 
 
 <h2 id="nowarning"> Permissions that don't cause warnings </h2>
 
 <p>
 The following permissions don't result in a warning:
 </p>
 
 <ul>
+  <li>"activeTab"</li>
   <li>"browsingData"</li>
   <li>"chrome://favicon/"</li>
   <li>"clipboardWrite"</li>
   <li>"contextMenus"</li>
   <li>"cookies"</li>
   <li>"experimental"</li>
   <li>"idle"</li>
   <li>"notifications"</li>
   <li>"storage"</li>
   <li>"unlimitedStorage"</li>
@@ skipping 27 matching lines @@
 (and all other extensions that have outstanding updates)
 by clicking the <b>chrome://extensions</b> page's
 <b>Update extensions now</b> button.
 </p>
 
 <h2 id="api">API</h2>
 
 <p>
 You can get a list of permission warnings for any manifest with
 <a href="management.html#method-getPermissionWarnings">chrome.management.getPermissionWarnings()</a>.
-</p>
+</p>