Add getDefaultFontSize and setDefaultFontSize to Font Settings Extension API.

chrome/test/data/extensions/api_test/font_settings/test.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.
 
 // Font settings API test
 // Run with browser_tests --gtest_filter=ExtensionApiTest.FontSettings
 
 var fs = chrome.experimental.fontSettings;
 
 function expect(expected, message) {
@@ skipping 38 matching lines @@
 
   function getFontList() {
     var message = 'getFontList should return an array of objects with ' +
         'fontName and localizedName properties.';
     fs.getFontList(chrome.test.callbackPass(function(value) {
       chrome.test.assertTrue(value.length > 0,
                              "Font list is not expected to be empty.");
       chrome.test.assertEq('string', typeof(value[0].fontName), message);
       chrome.test.assertEq('string', typeof(value[0].localizedName), message);
     }));
+  },
+
+  function setDefaultFontSize() {
+    fs.setDefaultFontSize({
+      pixelSize: 22
+    }, chrome.test.callbackPass());
+  },
+
+  function getDefaultFontSize() {
+    var expected = 22;
+    var message = 'Setting for default font size should be ' + expected;
+    fs.getDefaultFontSize({}, expect({pixelSize: expected}, message));
   }
 ]);