Update old syntax for action default_icon to populate 19 and 38px icons

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

 <p>
 Some examples:
 </p>
 <ul>
   <li> Subscribe to this page's RSS feed </li>
   <li> Make a slideshow out of this page's photos </li>
 </ul>
 
 <p>
 The RSS icon in the following screenshot
@@ skipping 39 matching lines @@
 can lose detail or make it look fuzzy. The old syntax for registering the
 default icon is still supported:
 </p>
 
 <pre data-filename="manifest.json">
 {
   "name": "My extension",
   ...
   <b>"page_action": {
     ...
-    "default_icon": "images/icon19.png"  <em>// optional</em>
-    <em>// equivalent to "default_icon": { "19": "images/icon19.png" }</em>
+    "default_icon": "images/icon38.png"  <em>// optional</em>
+    <em>// equivalent to "default_icon": { "38": "images/icon38.png" }</em>
   }</b>,
   ...
 }</pre>
 
 <h2 id="ui">Parts of the UI</h2>
 
 <p>
 Like browser actions,
 page actions can have an icon,
 a tooltip, and popup;
@@ skipping 40 matching lines @@
 
 <h2 id="examples"> Examples </h2>
 
 <p>
 You can find simple examples of using page actions in the
 <a href="http://src.chromium.org/viewvc/chrome/trunk/src/chrome/common/extensions/docs/examples/api/pageAction/">examples/api/pageAction</a>
 directory.
 For other examples and for help in viewing the source code, see
 <a href="samples">Samples</a>.
 </p>