[Extensions Sync] Don't apply sync data for unsyncable extensions

chrome/browser/extensions/extension_sync_service.cc

 // Copyright 2013 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_sync_service.h"
 
 #include <utility>
 
 #include "base/auto_reset.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 299 matching lines @@
     // If we'll re-enable the extension once it's updated, also send that back
     // to sync.
     if (it->second.grant_permissions_and_reenable)
       result.set_enabled(true);
   }
   return result;
 }
 
 void ExtensionSyncService::ApplySyncData(
     const ExtensionSyncData& extension_sync_data) {
+  const std::string& id = extension_sync_data.id();
+  // Note: |extension| may be null if it hasn't been installed yet.
+  const Extension* extension =
+      ExtensionRegistry::Get(profile_)->GetInstalledExtension(id);
+  // If there is an existing extension that shouldn't be sync'd, don't
+  // apply this sync data. This can happen if the local version of an
+  // extension is default-installed, but the sync server has data from another
+  // (non-default-installed) installation. We can't apply the sync data because
+  // it would always override the local state (which would never get sync'd).
+  // See crbug.com/731824.
+  if (extension && !ShouldSync(*extension))
+    return;
+
   // Ignore any pref change notifications etc. while we're applying incoming
   // sync data, so that we don't end up notifying ourselves.
   base::AutoReset<bool> ignore_updates(&ignore_updates_, true);
 
   // Note: this may cause an existing version of the extension to be reloaded.
   extensions::util::SetWasInstalledByCustodian(
       extension_sync_data.id(), profile_,
       extension_sync_data.installed_by_custodian());
 
   syncer::ModelType type = extension_sync_data.is_app() ? syncer::APPS
                                                         : syncer::EXTENSIONS;
-  const std::string& id = extension_sync_data.id();
   SyncBundle* bundle = GetSyncBundle(type);
   DCHECK(bundle->IsSyncing());
-  // Note: |extension| may be null if it hasn't been installed yet.
-  const Extension* extension =
-      ExtensionRegistry::Get(profile_)->GetInstalledExtension(id);
   if (extension && !IsCorrectSyncType(*extension, type)) {
     // The installed item isn't the same type as the sync data item, so we need
     // to remove the sync data item; otherwise it will be a zombie that will
     // keep coming back even if the installed item with this id is uninstalled.
     // First tell the bundle about the extension, so that it won't just ignore
     // the deletion, then push the deletion.
     bundle->ApplySyncData(extension_sync_data);
     bundle->PushSyncDeletion(id, extension_sync_data.GetSyncData());
     return;
   }
@@ skipping 367 matching lines @@
       sync_data_list->push_back(CreateSyncData(*extension));
     }
   }
 }
 
 bool ExtensionSyncService::ShouldSync(const Extension& extension) const {
   // Themes are handled by the ThemeSyncableService.
   return extensions::util::ShouldSync(&extension, profile_) &&
          !extension.is_theme();
 }