Move context menu module out of experimental.

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

+<!-- BEGIN AUTHORED CONTENT -->
+<p>
+The context menus module allows you
+to add items to Chrome's context menu.
+</p>
+
+<p>
+You can choose what types of objects
+your context menu additions apply to,
+such as images, hyperlinks, and pages.
+</P>
+
+<p>
+You can create as many context menu items
+as you need, but if more than one
+from your extension is visible at once,
+Google Chrome automatically collapses them
+into a single parent menu.
+</p>
+
+<h2 id="manifest">Manifest</h2>
+<p>You must declare the "contextMenus" permission
+in your extension's manifest to use the API.
+Also, you should specify a 16x16-pixel icon
+for display next to your menu item.
+For example:
+</p>
+
+<pre>{
+  "name": "My extension",
+  ...
+  "permissions": [
+    <b>"contextMenus"</b>
+  ],
+  "icons": {
+    <b>"16": "icon-bitty.png",</b>
+    "48": "icon-small.png",
+    "128": "icon-large.png"
+  },
+  ...
+}</pre>
+
+<!-- END AUTHORED CONTENT -->