[MD settings] unit test for incognito activation

chrome/test/data/webui/settings/test_site_settings_prefs_browser_proxy.js

Index: chrome/test/data/webui/settings/test_site_settings_prefs_browser_proxy.js
diff --git a/chrome/test/data/webui/settings/test_site_settings_prefs_browser_proxy.js b/chrome/test/data/webui/settings/test_site_settings_prefs_browser_proxy.js
index 6fe9b1ca4a670e19f9e30d280c432135acc73109..ef7069b910a07af76810c9ecb0700fe7e5603a57 100644
--- a/chrome/test/data/webui/settings/test_site_settings_prefs_browser_proxy.js
+++ b/chrome/test/data/webui/settings/test_site_settings_prefs_browser_proxy.js
@@ -67,6 +67,9 @@ var TestSiteSettingsPrefsBrowserProxy = function() {
     'setProtocolDefault'
   ]);
 
+  /** @private {boolean} */
+  this.hasIncognito = false;
+
   /** @private {!SiteSettingsPref} */
   this.prefs_ = prefsEmpty;
 
@@ -90,6 +93,15 @@ TestSiteSettingsPrefsBrowserProxy.prototype = {
   __proto__: settings.TestBrowserProxy.prototype,
 
   /**
+   * Pretends an incognito session started or ended.
+   * @param {boolean} hasIncognito True for session started.
+   */
+  setIncognito: function(hasIncognito) {
+    this.hasIncognito = hasIncognito;
+    cr.webUIListenerCallback('onIncognitoStatusChanged', hasIncognito);
+  },
+
+  /**
    * Sets the prefs to use when testing.
    * @param {!SiteSettingsPref} prefs The prefs to set.
    */
@@ -231,6 +243,14 @@ TestSiteSettingsPrefsBrowserProxy.prototype = {
       console.log('getExceptionList received unknown category: ' + contentType);
 
     assert(pref != undefined, 'Pref is missing for ' + contentType);
+
+    if (this.hasIncognito) {
+      pref = pref.concat(pref.filter(function(p) {

[dpapad, 2017/03/23 22:29:10]

I am confused about the usage of filter() here. filter() is expected to return
either true or false to signify what stays and what is dropped. Here we are
returning either an Object or undefined. Should it simply be 

pref = pref.concat(pref.filter(function(p) { return p.source == 'policy'; }));

[dschuyler, 2017/03/23 23:54:36]

filter() returns the object returned by the function.

I've changed this to a loop so that the incognito flag is set correctly.

+        if (p.source == 'policy')
+          return Object.assign({incognito: true}, p);
+      }));
+    }
+
     return Promise.resolve(pref);
   },