Add docs for chrome.wallpaper API

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

+<h2 id="manifest">Manifest</h2>
+<p>You must declare the "wallpaper" permission in the app
+<a href="manifest.html">manifest</a> to use the wallpaper API. If you use the
+'url' property of setWallpaper, you must also specify
+<a href="declare_permissions.html">host permissions</a> for the URL in the

[not at google - send to devlin, 2013/10/17 18:18:20]

move this into permissions/wallpaper.html

[bshe, 2013/10/17 20:32:18]

It looks like the permissions/wallpaper.html should only describe the permission
itself? I added the file and described the wallpaper permission in that file.

On 2013/10/17 18:18:20, kalman wrote:

+manifest.
+For example:</p>
+<pre data-filename="manifest.json">
+{
+  "name": "My extension",
+  ...
+  <b>"permissions": [
+    "wallpaper",
+    "http://example.com/*"
+  ]</b>,
+  ...
+}</pre>
+
+<h2 id="overview-examples">Examples</h2>
+
+<p>
+For example, to set the wallpaper as the image at
+<code>http://example.com/a_file.png</code>, you can call
+<code>chrome.wallpaper.setWallpaper</code> this way:
+</p>
+
+<pre>
+chrome.wallpaper.setWallpaper(
+    {
+      'url': 'http://example.com/a_file.jpg',
+      'layout': 'CENTER_CROPPED',
+      'name': 'test_wallpaper'
+    }, function() { console.error(chrome.runtime.lastError.message); });

[not at google - send to devlin, 2013/10/17 18:18:20]

why are you printing out the error? is this function likely to throw an error? I
assume not.

[bshe, 2013/10/17 20:32:18]

If the XMLRequest failed (user forgot to specify host permission) or the url is
not an image, it could throw errors. I put is here just to show that we can get
error message from chrome.runtime.lastError. But it is probably not necessary
here in the doc?

On 2013/10/17 18:18:20, kalman wrote:

+</pre>