Add 5 experimental accessibility features on Chrome OS.

chrome/browser/resources/settings/a11y_page/a11y_page.js

Index: chrome/browser/resources/settings/a11y_page/a11y_page.js
diff --git a/chrome/browser/resources/settings/a11y_page/a11y_page.js b/chrome/browser/resources/settings/a11y_page/a11y_page.js
index dbb55f3f747e6407480ddd447ed4ee513987e435..33499cd97b98d26c37c33f35fb394841d7ea5bb2 100644
--- a/chrome/browser/resources/settings/a11y_page/a11y_page.js
+++ b/chrome/browser/resources/settings/a11y_page/a11y_page.js
@@ -25,6 +25,9 @@ Polymer({
       type: Object,
       notify: true,
     },
+
+    /** @private Whether to show experimental accessibility features. */
+    showExperimentalFeatures_: Boolean,

[Dan Beam, 2016/03/11 22:07:20]

I think this is all you need:

/**
 * Whether to show experimental accessibility features.
 * @private {boolean}
 */
showExperimentalFeatures_: {
  type: Boolean,
  value: function() {
    return loadTimeData.getBoolean('enableExperimentalA11yFeatures');
  },
},

   },
 
   /** @private */
@@ -32,4 +35,20 @@ Polymer({
     window.open(
         'https://chrome.google.com/webstore/category/collection/accessibility');
   },
+
+  /** @override */
+  ready: function() {
+    cr.addWebUIListener('show-experimental-features',
+                        this.onShowExperimentalFeatures_.bind(this));
+    chrome.send('initializeAccessibilityPage');
+  },
+
+  /**
+   * Handler for updating whether experimental accessibility features
+   * should be shown.

[Dan Beam, 2016/03/11 22:07:20]

@param {boolean} show ...

+   * @private
+   */
+  onShowExperimentalFeatures_: function(show) {
+    this.showExperimentalFeatures_ = show;
+  },
 });