Implement the API index doc for platform apps.

chrome/common/extensions/docs/static/apps_api_index.html

Index: chrome/common/extensions/docs/static/apps_api_index.html
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+<div id="pageData-name" class="pageData">chrome.* APIs</div>
+<div id="pageData-showTOC" class="pageData">true</div>
+
+<h2 id="supported">Supported APIs</h2>
+
+<p>
+Packaged apps can call some of the stable APIs from the extension system.
+</p>
+
+<ul>
+  <li jsselect="listChromeAPIs('platform_app', false);"><a jsvalues=".href: $this + '.html'" jscontent="$this" href="bookmarks.html" js>bookmarks</a>
+  </li>
+</ul>
+
+<h2 id="experimental">Experimental APIs</h2>
+
+<p>
+Packaged apps can also use any experimental extension API.
+</p>
+
+<ul>
+  <li jsselect="listChromeAPIs('platform_app', true);"><a jsvalues=".href: $this + '.html'" jscontent="$this" href="bookmarks.html" js>bookmarks</a>
+  </li>
+</ul>
+
+<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>