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

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

 <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>
 <ul>
   <li> Subscribe to this page's RSS feed </li>
   <li> Make a slideshow out of this page's photos </li>
@@ skipping 25 matching lines @@
 <p>
 Register your page action in the
 <a href="manifest.html">extension manifest</a>
 like this:
 </p>
 
 <pre>{
   "name": "My extension",
   ...
   <b>"page_action": {
-    "default_icon": "icons/foo.png", <em>// optional</em>
-    "default_title": "Do action",    <em>// optional; shown in tooltip</em>
-    "default_popup": "popup.html"    <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>"page_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>
 Like browser actions,
 page actions can have an icon,
 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
@@ skipping 36 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.html">Samples</a>.
-</p>
+</p>