Move history API out of experimental. Allow extensions to override history page.

chrome/common/extensions/docs/template/api_template.html

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       <!-- SUBTEMPLATES: DO NOT MOVE FROM THIS LOCATION -->
       <!-- In particular, sub-templates that recurse, must be used by allowing
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                   <li><a href="options.html">Options Pages</a></li>
                   <li><a href="override.html">Override Pages</a></li>
                   <li><a href="pageAction.html">Page Actions</a></li>
                   <li><a href="themes.html">Themes</a></li>
                 </ul>
               </li>
               <li>Browser Interaction
                 <ul>
                   <li><a href="bookmarks.html">Bookmarks</a></li>
                   <li><a href="events.html">Events</a></li>
+                  <li><a href="history.html">History</a></li>
                   <li><a href="tabs.html">Tabs</a></li>
                   <li><a href="windows.html">Windows</a></li>
                 </ul>
               </li>
               <li>Implementation
                 <ul>
                   <li><a href="background_pages.html">Background Pages</a></li>
                   <li><a href="content_scripts.html">Content Scripts</a></li>
                   <li><a href="xhr.html">Cross-Origin XHR</a></li>
                   <li><a href="i18n.html">Internationalization</a></li>
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     _uff=0;
     urchinTracker();
   }
   catch(e) {/* urchinTracker not available. */}
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