chrome/common/extensions/docs/templates/intros/downloads.html

<h2 id='manifest'>Manifest</h2>

<p> You must declare the 'downloads' permission in the <a
href='manifest.html'>extension manifest</a> to use this API, along with <a
href='declare_permissions.html'>host permissions</a> for any hosts that you
may pass to $ref:downloads.download.</p>

<pre>{
  'name': 'My extension',
  ...
<b>  'permissions': [
    'downloads',
    '*://*.google.com'
  ]</b>,
  ...
}</pre>

<p>If the URL's hostname is not specified in the permissions, then 
$ref:downloads.download will call its callback with a null
<code>downloadId</code> and set the 
$ref:runtime.lastError
object to indicate that the extension does not have permission to access that
hostname.</p>

<h2 id='examples'>Examples</h2>

<p>You can find simple examples of using the downloads module in the <a
href='http://src.chromium.org/viewvc/chrome/trunk/src/chrome/common/extensions/docs/examples/api/downloads/'>examples/api/downloads</a>
directory. For other examples and for help in viewing the source code, see <a
href='samples.html'>Samples</a>.</p>