add setBoolPref(prefName, newValue) to allow browser based tests to get/set preferences

js/tests/js1_5/browser.js

@@ -135,3 +135,39 @@ function quit()
 }
 
 window.onerror = reportFailure;
+
+var gPrivileges = 'UniversalXPConnect';
+
+function setBoolPref(prefName, newValue)
+{
+  var prevValue = false;
+
+  try
+  {
+    netscape.security.PrivilegeManager.
+      enablePrivilege(gPrivileges);
+
+    var preferences = Components.classes['@mozilla.org/preferences;1'];
+    if (preferences)
+    {
+      var prefService = preferences.
+                         getService(Components.interfaces.nsIPrefService);
+      var pref = prefService.getBranch('');
+      try
+      {
+        prevValue = pref.getBoolPref(prefName);
+      }
+      catch(eget)
+      {
+        writeLineToLog('Unable to get preference ' +  prefName);
+      }
+      pref.setBoolPref(prefName, newValue);
+    }
+  }
+  catch (e)
+  {
+    writeLineToLog('Unable to set preference ' + 
+                   prefName + ' to ' + prevValue);
+  }
+  return prevValue;
+}