Remove .html extension from links

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

 <h1 class="page_title">JavaScript APIs</h1>
 <p class="doc-family apps">
 Chrome provides {{platform}}s with many special-purpose APIs like
 <code>chrome.runtime</code> and <code>chrome.alarms</code>.
 </p>
 
 {{?stable_apis}}
 <h2 id="stable_apis">Stable APIs</h2>
 <p>
 {{+partials.api_table apis:stable_apis is_stable:true/}}
@@ skipping 10 matching lines @@
 {{?dev_apis}}
 <h2 id="dev_apis">Dev APIs</h2>
 <p>These APIs are only available in the Chrome Dev channel:
 {{+partials.api_table apis:dev_apis is_stable:false/}}
 </p>
 {{/dev_apis}}
 
 <h2 id="experimental">Experimental APIs</h2>
 <p>
 Chrome also has
-<a href="experimental.html">experimental APIs</a>,
+<a href="experimental">experimental APIs</a>,
 some of which will become supported APIs
 in future releases of Chrome.
 </p>
 
 <h2 id="conventions">API conventions</h2>
 
 <p>
 Unless the doc says otherwise,
 methods in the chrome.* APIs are <b>asynchronous</b>:
 they return immediately,
 without waiting for the operation to finish.
 If you need to know the outcome of an operation,
 then you pass a callback function into the method.
 For more information, watch this video:
 </p>
 
 <p class="doc-family extensions">
 <iframe title="YouTube video player" width="640" height="390" src="//www.youtube.com/embed/bmxr75CV36A?rel=0" frameborder="0" allowfullscreen></iframe>
 </p>