Change browser/page action default icon defined in manifest to support hidpi.

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

 <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>,
   and a <a href="#popups">popup</a>.
   </p>
 
@@ skipping 26 matching lines @@
 <p>
 Register your browser action in the
 <a href="manifest.html">extension manifest</a>
 like this:
 </p>
 
 <pre>{
   "name": "My extension",
   ...
   <b>"browser_action": {
-    "default_icon": "images/icon19.png", <em>// optional</em>
+    "default_icon": {                    <em>// optional</em>
+      "19": "images/icon19.png",           <em>// optional</em>
+      "38": "images/icon38.png"            <em>// optional</em>
+    },
     "default_title": "Google Mail",      <em>// optional; shown in tooltip</em>
     "default_popup": "popup.html"        <em>// optional</em>
   }</b>,
   ...
 }</pre>
 
+<p>
+If you only provide one of the 19px or 38px icon size, the extension system will
+scale the icon you provide to the pixel density of the user's display, which
+can lose detail or make it look fuzzy. The old syntax for registering the
+default icon is still supported:
+</p>
+
+<pre>{
+  "name": "My extension",
+  ...
+  <b>"browser_action": {
+    ...
+    "default_icon": "images/icon19.png"  <em>// optional</em>
+    <em>// equivalent to "default_icon": { "19": "images/icon19.png" }</em>
+  }</b>,
+  ...
+}</pre>
+
 <h2 id="ui">Parts of the UI</h2>
 
 <p>
 A browser action can have an <a href="#icon">icon</a>,
 a <a href="#tooltip">tooltip</a>,
 a <a href="#badge">badge</a>,
 and a <a href="#popups">popup</a>.
 </p>
 
 <h3 id="icon">Icon</h3>
 
-<p>Browser action icons can be up to 19 pixels wide and high.
-  Larger icons are resized to fit, but for best results,
-  use a 19-pixel square icon.</p>
+<p>Browser action icons can be up to 19 dips (device-independent pixels)
+  wide and high. Larger icons are resized to fit, but for best results,
+  use a 19-dip square icon.</p>
 
 <p>You can set the icon in two ways:
   using a static image or using the
   HTML5 <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html">canvas element</a>.
   Using static images is easier for simple applications,
   but you can create more dynamic UIs &mdash;
   such as smooth animation &mdash;
   using the canvas element.
   </p>
 
 <p>Static images can be in any format WebKit can display,
   including BMP, GIF, ICO, JPEG, or PNG.
   </p>
 
 <p>To set the icon,
-use the <b>default_icon</b> field of <b>browser_action</b>
-in the <a href="#manifest">manifest</a>,
-or call the <a href="#method-setIcon">setIcon()</a> method.
+  use the <b>default_icon</b> field of <b>browser_action</b>
+  in the <a href="#manifest">manifest</a>,
+  or call the <a href="#method-setIcon">setIcon()</a> method.
+  </p>
 
+<p>To properly display icon when screen pixel density (ratio
+  <code>size_in_pixel / size_in_dip</code>) is different than 1,
+  the icon can be defined as set of images with different sizes.
+  The actual image to display will be selected from the set to
+  best fit the pixel size of 19 dip icon.
+  At the moment, the icon set can contain images with pixel sizes 19 and 38.
+  </p>
 
 <h3 id="tooltip">Tooltip</h3>
 
 <p>
 To set the tooltip,
 use the <b>default_title</b> field of <b>browser_action</b>
 in the <a href="#manifest">manifest</a>,
 or call the <a href="#method-setTitle">setTitle()</a> method.
 You can specify locale-specific strings for the <b>default_title</b> field;
 see <a href="i18n.html">Internationalization</a> for details.
@@ skipping 65 matching lines @@
 </ul>
 
 <h2 id="examples"> Examples </h2>
 
 <p>
 You can find simple examples of using browser actions in the
 <a href="http://src.chromium.org/viewvc/chrome/trunk/src/chrome/common/extensions/docs/examples/api/browserAction/">examples/api/browserAction</a>
 directory.
 For other examples and for help in viewing the source code, see
 <a href="samples.html">Samples</a>.
-</p>
+</p>