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 ffd838e4a2c7fa0d24f777617a75f8a37c5b43be..cc46f5d865b4be9ecba299f2ad5a2f5c16652b4d 100644
--- a/chrome/browser/resources/options/browser_options.js
+++ b/chrome/browser/resources/options/browser_options.js
@@ -86,6 +86,9 @@ cr.define('options', function() {
       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);
@@ -169,6 +172,34 @@ cr.define('options', function() {
     },
 
     /**
+     * Called when the value of the instant.enabled preference changes. Request
+     * the state of the Instant field trial experiment.
+     * @param {Event} event Change event.
+     * @private
+     */
+    onInstantEnabledChanged_: function(event) {
+      chrome.send('getInstantFieldTrialStatus');
+    },
+
+    /**
+     * Called to set the Instant field trial status.
+     * @param {boolean} enabled If true, the experiment is enabled.
+     * @private
+     */
+    setInstantFieldTrialStatus_: function(enabled) {
+      var experiment_checkbox = $('instantFieldTrialCheckbox');
+      var preference_checkbox = $('instantEnabledCheckbox');
+      if (enabled) {
+        experiment_checkbox.checked = true;

[Evan Stade, 2011/07/26 00:10:21]

this should always start as true. Thus it can be part of the html, no?

[sreeram, 2011/07/26 02:45:53]

Done.

+        experiment_checkbox.style.display = "inline";
+        preference_checkbox.style.display = "none";

[Evan Stade, 2011/07/26 00:10:21]

foo.hidden = true/false

[sreeram, 2011/07/26 02:45:53]

Done.

+      } else {
+        experiment_checkbox.style.display = "none";
+        preference_checkbox.style.display = "inline";
+      }
+    },
+
+    /**
      * 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
@@ -489,6 +520,10 @@ cr.define('options', function() {
     BrowserOptions.getInstance().updateAutocompleteSuggestions_(suggestions);
   };
 
+  BrowserOptions.setInstantFieldTrialStatus = function(enabled) {
+    BrowserOptions.getInstance().setInstantFieldTrialStatus_(enabled);
+  };
+
   // Export
   return {
     BrowserOptions: BrowserOptions