Refactor the various ways to control what users can do to extensions.

chrome/browser/extensions/crx_installer.cc

Index: chrome/browser/extensions/crx_installer.cc
===================================================================
--- chrome/browser/extensions/crx_installer.cc	(revision 138227)
+++ chrome/browser/extensions/crx_installer.cc	(working copy)
@@ -26,6 +26,7 @@
 #include "chrome/browser/extensions/default_apps_trial.h"
 #include "chrome/browser/extensions/extension_error_reporter.h"
 #include "chrome/browser/extensions/extension_service.h"
+#include "chrome/browser/extensions/extension_system.h"
 #include "chrome/browser/extensions/permissions_updater.h"
 #include "chrome/browser/extensions/webstore_installer.h"
 #include "chrome/browser/profiles/profile.h"
@@ -347,12 +348,10 @@
     return;
   }
 
-  if (!frontend_weak_->extension_prefs()->IsExtensionAllowedByPolicy(
-          extension_->id(), install_source_)) {
-    ReportFailureFromUIThread(l10n_util::GetStringFUTF16(
-        IDS_EXTENSION_CANT_INSTALL_POLICY_BLACKLIST,
-        UTF8ToUTF16(extension_->name()),
-        UTF8ToUTF16(extension_->id())));
+  string16 error;
+  if (!ExtensionSystem::Get(profile_)->management_policy()->UserMayLoad(
+      extension_, install_source_, &error)) {
+    ReportFailureFromUIThread(error);
     return;
   }