Extensions installed by policy overrun previously installed extensions.

chrome/browser/extensions/extension_updater.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/extensions/extension_updater.h"
 
 #include <algorithm>
 #include <set>
 
 #include "base/compiler_specific.h"
@@ skipping 982 matching lines @@
   DCHECK(will_check_soon_);
   CheckNow();
   will_check_soon_ = false;
 }
 
 void ExtensionUpdater::CheckNow() {
   DCHECK(alive_);
   NotifyStarted();
   ManifestFetchesBuilder fetches_builder(service_, extension_prefs_);
 
-  const ExtensionList* extensions = service_->extensions();
-  for (ExtensionList::const_iterator iter = extensions->begin();
-       iter != extensions->end(); ++iter) {
-    fetches_builder.AddExtension(**iter);
-  }
-
   const PendingExtensionManager* pending_extension_manager =
       service_->pending_extension_manager();
+  std::set<std::string> pending_ids;
 
   PendingExtensionManager::const_iterator iter;
   for (iter = pending_extension_manager->begin();
        iter != pending_extension_manager->end(); iter++) {
     // TODO(skerner): Move the determination of what gets fetched into
     // class PendingExtensionManager.
     Extension::Location location = iter->second.install_source();
     if (location != Extension::EXTERNAL_PREF &&
-        location != Extension::EXTERNAL_REGISTRY)
+        location != Extension::EXTERNAL_REGISTRY) {
       fetches_builder.AddPendingExtension(iter->first, iter->second);
+      pending_ids.insert(iter->first);
+    }
+  }
+
+  const ExtensionList* extensions = service_->extensions();
+  for (ExtensionList::const_iterator iter = extensions->begin();
+       iter != extensions->end(); ++iter) {
+    // An extension might be overwritten by policy, and have its update url
+    // changed. Make sure existing extensions aren't fetched again, if a
+    // pending fetch for an extension with the same id already exists.
+    if (!ContainsKey(pending_ids, (*iter)->id())) {
+      fetches_builder.AddExtension(**iter);
+    }
   }
 
   fetches_builder.ReportStats();
 
   std::vector<ManifestFetchData*> fetches(fetches_builder.GetFetches());
 
   // Start a fetch of the blacklist if needed.
   if (blacklist_checks_enabled_) {
     // Note: it is very important that we use  the https version of the update
     // url here to avoid DNS hijacking of the blacklist, which is not validated
@@ skipping 203 matching lines @@
   std::set<std::string>::const_iterator i;
   for (i = ids.begin(); i != ids.end(); ++i)
     in_progress_ids_.insert(*i);
 }
 
 void ExtensionUpdater::RemoveFromInProgress(const std::set<std::string>& ids) {
   std::set<std::string>::const_iterator i;
   for (i = ids.begin(); i != ids.end(); ++i)
     in_progress_ids_.erase(*i);
 }