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

<div id="pageData-name" class="pageData">chrome.* APIs</div>

<p>
Google Chrome provides APIs such as
<code>chrome.bookmarks</code> and <code>chrome.tab</code>
so that extensions can interact with the browser.
Here are the supported chrome.* APIs:
</p>

<ul>
  <li><a href="bookmarks.html">bookmarks</a></li>
  <li><a href="browserAction.html">browserAction</a></li>
  <li><a href="extension.html">extension</a></li>
  <li><a href="i18n.html">i18n</a></li>
  <li><a href="pageAction.html">pageAction</a></li>
  <li><a href="tabs.html">tabs</a></li>
  <li><a href="windows.html">windows</a></li>
</ul>

<p>
Unless the doc says otherwise,
methods in the chrome.* APIs are asynchronous:
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.
<!-- [PENDING: update/elaborate on that] -->
</p>