Introduce a field trial for Instant.

chrome/browser/resources/options/browser_options.js

Index: chrome/browser/resources/options/browser_options.js
diff --git a/chrome/browser/resources/options/browser_options.js b/chrome/browser/resources/options/browser_options.js
index 9a043143cc7d1fcc8cd3d17c6ddec8272421ef3a..050cef51043c00b957cf9ed42093cbf785b507e0 100644
--- a/chrome/browser/resources/options/browser_options.js
+++ b/chrome/browser/resources/options/browser_options.js
@@ -71,18 +71,24 @@ cr.define('options', function() {
       $('defaultSearchEngine').onchange = this.setDefaultSearchEngine_;
 
       var self = this;
-      $('instantEnableCheckbox').onclick = function(event) {
-        if (this.checked && !self.instantConfirmDialogShown_) {
-          // Leave disabled for now. The PrefCheckbox handler already set it to
-          // true so undo that.
-          Preferences.setBooleanPref(this.pref, false, this.metric);
-          OptionsPage.navigateToPage('instantConfirm');
+      $('instantEnabledCheckbox').onclick = function(event) {
+        if (this.checked) {
+          if (self.instantConfirmDialogShown_) {
+            chrome.send('enableInstant');
+          } else {
+            OptionsPage.navigateToPage('instantConfirm');
+          }
+        } else {
+          chrome.send('disableInstant');
         }
       };
 
       Preferences.getInstance().addEventListener('instant.confirm_dialog_shown',
           this.onInstantConfirmDialogShownChanged_.bind(this));
 
+      Preferences.getInstance().addEventListener('instant.enabled',
+          this.onInstantEnabledChanged_.bind(this));
+
       var homepageField = $('homepageURL');
       $('homepageUseNTPButton').onchange =
           this.handleHomepageUseNTPButtonChange_.bind(this);
@@ -166,6 +172,29 @@ cr.define('options', function() {
     },
 
     /**
+     * Called when the value of the instant.enabled preference changes. Update
+     * the state of the checkbox.
+     * @param {Event} event Change event.
+     * @private
+     */
+    onInstantEnabledChanged_: function(event) {
+      var checkbox = $('instantEnabledCheckbox');
+      checkbox.checked = event.value['value'];
+      checkbox.disabled = event.value['managed'];
+
+      chrome.send('isInstantFieldTrialExperimentGroup');
+    },
+
+    /**
+     * Called to inform that the user has been selected into the Instant field
+     * trial experiment group (see instant_field_trial.h).
+     * @private
+     */
+    setInstantFieldTrialExperimentGroup_: function() {
+      $('instantEnabledCheckbox').checked = true;
+    },
+
+    /**
      * Update the Default Browsers section based on the current state.
      * @param {string} statusString Description of the current default state.
      * @param {boolean} isDefault Whether or not the browser is currently
@@ -486,6 +515,10 @@ cr.define('options', function() {
     BrowserOptions.getInstance().updateAutocompleteSuggestions_(suggestions);
   };
 
+  BrowserOptions.setInstantFieldTrialExperimentGroup = function() {
+    BrowserOptions.getInstance().setInstantFieldTrialExperimentGroup_();
+  };
+
   // Export
   return {
     BrowserOptions: BrowserOptions