Do not attempt to apply app sync updates to extensions with matching ID, or vice versa.

chrome/browser/extensions/extension_service.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_service.h"
 
 #include <algorithm>
 #include <set>
 
 #include "base/basictypes.h"
@@ skipping 1620 matching lines @@
   GetSyncDataListHelper(disabled_extensions_, filter, &sync_data_list);
   GetSyncDataListHelper(terminated_extensions_, filter, &sync_data_list);
   return sync_data_list;
 }
 
 void ExtensionService::ProcessSyncData(
     const ExtensionSyncData& extension_sync_data,
     ExtensionFilter filter) {
   const std::string& id = extension_sync_data.id;
 
+  // If we have an app update for an extension, or vice versa, ignore it.
+  //
+  // This can happen if an app author publishes an update that is actually an
+  // extension, for example.
+  const Extension* extension_if_installed =
+      GetExtensionByIdInternal(id, true, true, true);
+  if (extension_if_installed && !filter(*extension_if_installed)) {
+    LOG(WARNING) << "Attempt to sync wrong type of extension for " << id;
+    return;
+  }
+
   // Handle uninstalls first.
   if (extension_sync_data.uninstalled) {
     std::string error;
     if (!UninstallExtensionHelper(this, id)) {
       LOG(WARNING) << "Could not uninstall extension " << id
                    << " for sync";
     }
     return;
   }
 
@@ skipping 883 matching lines @@
 
 ExtensionService::NaClModuleInfoList::iterator
     ExtensionService::FindNaClModule(const GURL& url) {
   for (NaClModuleInfoList::iterator iter = nacl_module_list_.begin();
        iter != nacl_module_list_.end(); ++iter) {
     if (iter->url == url)
       return iter;
   }
   return nacl_module_list_.end();
 }