Docs polish

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

 <div id="pageData-title" class="pageData">Browser Actions</div>
 
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 <p>Use browser actions to put icons
   in the main Google Chrome toolbar,
   to the right of the address bar.
   In addition to its <a href="#icon">icon</a>,
   a browser action can also have
   a <a href="#tooltip">tooltip</a>,
   a <a href="#badge">badge</a>,
@@ skipping 23 matching lines @@
 
 <h2 id="manifest">Manifest</h2>
 
 <p>
 Register your browser action in the
 <a href="manifest.html">extension manifest</a>
 like this:
 </p>
 
 <pre>"browser_action": {
+  "default_icon": "images/icon19.png", <em>// <b>required</b></em>
   "default_title": "Google Mail",      <em>// optional; shown in tooltip</em>
-  "default_icon": "images/icon19.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>browser_action</b> entry in the manifest
-  so that the system reserves space
-  for your browser action in the toolbar.</p>
-
 <h2 id="ui">Parts of the UI</h2>
 
 <p>
 A browser action must have an <a href="#icon">icon</a>.
 It can also have
 a <a href="#tooltip">tooltip</a>,
 a <a href="#badge">badge</a>,
 and a <a href="#popup">popup</a>.
 </p>
 
@@ skipping 91 matching lines @@
   <li><b>Do</b> use alpha transparency
     to add soft edges to your icon.
     Because many people use themes,
     your icon should look nice
     on a variety of background colors.
   <li><b>Don't</b> constantly animate your icon.
     That's just annoying.
 </ul>
 
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