Docs polish

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

 <div id="pageData-title" class="pageData">Page Actions</div>
 
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 <p>
 Use page actions to put icons inside the address bar.
 Page actions represent actions
 that can be taken on the current page,
 but that aren't applicable to all pages.
 Some examples:
 </p>
@@ skipping 20 matching lines @@
 
 <h2 id="manifest">Manifest</h2>
 
 <p>
 Register your page action in the
 <a href="manifest.html">extension manifest</a>
 like this:
 </p>
 
 <pre>"page_action": {
+  "default_icon": "icons/foo.png", <em>// <b>required</b></em>
   "default_title": "Do action",    <em>// optional; shown in tooltip</em>
-  "default_icon": "icons/foo.png", <em>// optional</em>
   "popup": "popup.html"            <em>// optional</em>
 }</pre>
 
-<p><b>Note:</b> Even if you don't include
-  any of the values,
-  you must include an empty <b>page_action</b> entry
-  in your manifest so that the system
-  reserves a slot for your page action
-  in the address bar.</p>
-
-<p>
-Set "default_icon" if at all possible.
-Users see the default icon when they install your extension,
-which helps them know what to look for when your page action
-is active for a given page.</p>
-
 <h2 id="ui">Parts of the UI</h2>
 
 <p>
 Like browser actions,
 page actions have an icon and
 can also have a tooltip and popup;
 they can't have badges, however.
 In addition, page actions can appear and disappear.
 You can find information about icons, tooltips, and popups
 by reading about the
@@ skipping 43 matching lines @@
     in the location bar
     are smaller than 19 pixels.
     If the edge pixels are used,
     they are usually only used
     for a faint shadow.
   <li><b>Don't</b> constantly animate your icon.
     That's just annoying.
 </ul>
 
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