Add a group policy controlling which sites can install extensions.

chrome/browser/policy/configuration_policy_handler_list.cc

Index: chrome/browser/policy/configuration_policy_handler_list.cc
diff --git a/chrome/browser/policy/configuration_policy_handler_list.cc b/chrome/browser/policy/configuration_policy_handler_list.cc
index b73caf7e9963131e305b5bb635402932c16a83c4..ab73c642d87fb4dee3b0392570041754806887c2 100644
--- a/chrome/browser/policy/configuration_policy_handler_list.cc
+++ b/chrome/browser/policy/configuration_policy_handler_list.cc
@@ -337,6 +337,11 @@ ConfigurationPolicyHandlerList::ConfigurationPolicyHandlerList() {
                                      prefs::kExtensionInstallDenyList,
                                      true));
 

[Mattias Nissler (ping if slow), 2012/06/08 09:38:22]

drop the newline here so all the extension handlers are in one block.

+  handlers_.push_back(
+      new ExtensionURLPatternListPolicyHandler(
+          key::kExtensionInstallSources,
+          prefs::kExtensionAllowedInstallSites));
+
 #if !defined(OS_CHROMEOS)
   handlers_.push_back(new DownloadDirPolicyHandler());
 #endif  // !defined(OS_CHROMEOS)