Add getDefaultFontSize and setDefaultFontSize to Font Settings Extension API.

chrome/common/extensions/docs/examples/api/fontSettings/popup.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 var scriptList;
 
 // Mapping between font list ids and the generic family setting they
 // represent.
 var genericFamilies = [
   { fontList: 'standardFontList', name: 'standard' },
@@ skipping 89 matching lines @@
     var details = {};
     details.genericFamily = family;
     if (script != DEFAULT_SCRIPT)
       details.script = script;
 
     chrome.experimental.fontSettings.getFontName(details,
                                                  getFontNameHandler(list));
   }
 }
 
+function defaultFontSizeChanged() {
+  var defaultFontSizeInput = document.getElementById('defaultFontSize');
+  var pixelSize = parseInt(defaultFontSizeInput.value);
+  if (!isNaN(pixelSize)) {
+    chrome.experimental.fontSettings.setDefaultFontSize({
+      pixelSize: pixelSize
+    });
+  }
+}
+
 function init() {
   scriptList = document.getElementById('scriptList');
   scriptList.addEventListener('change', updateListSelections);
 
   // Populate the font lists.
   chrome.experimental.fontSettings.getFontList(populateLists);
 
   // Add change handlers to the font lists.
   for (var i = 0; i < genericFamilies.length; i++) {
     var list = document.getElementById(genericFamilies[i].fontList);
     var handler = getFontChangeHandler(list, genericFamilies[i].name);
     list.addEventListener('change', handler);
   }
+
+  var defaultFontSizeInput = document.getElementById('defaultFontSize');
+  chrome.experimental.fontSettings.getDefaultFontSize({}, function(details) {
+    defaultFontSizeInput.value = details.pixelSize;
+  });
+  defaultFontSizeInput.addEventListener('change', defaultFontSizeChanged);
 }
 
 document.addEventListener('DOMContentLoaded', init);