Install CRX updates one at a time.

chrome/browser/extensions/test_extension_service.h

 // 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.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_TEST_EXTENSION_SERVICE_H_
 #define CHROME_BROWSER_EXTENSIONS_TEST_EXTENSION_SERVICE_H_
 #pragma once
 
 #include <string>
 #include <vector>
 
 #include "chrome/browser/extensions/extension_service.h"
 
+class CrxInstaller;
+
 // Implemention of ExtensionServiceInterface with default
 // implementations for methods that add failures.  You should subclass
 // this and override the methods you care about.
 class TestExtensionService : public ExtensionServiceInterface {
  public:
   virtual ~TestExtensionService();
 
   // ExtensionServiceInterface implementation.
   virtual const ExtensionList* extensions() const OVERRIDE;
   virtual PendingExtensionManager* pending_extension_manager() OVERRIDE;
-  virtual void UpdateExtension(const std::string& id,
-                               const FilePath& path,
-                               const GURL& download_url) OVERRIDE;
+
+  virtual bool UpdateExtension(
+      const std::string& id,
+      const FilePath& path,
+      const GURL& download_url,
+      CrxInstaller** out_crx_installer) OVERRIDE;
   virtual const Extension* GetExtensionById(
       const std::string& id, bool include_disabled) const OVERRIDE;
   virtual const Extension* GetInstalledExtension(
       const std::string& id) const OVERRIDE;
   virtual bool IsExtensionEnabled(
       const std::string& extension_id) const OVERRIDE;
   virtual bool IsExternalExtensionUninstalled(
       const std::string& extension_id) const OVERRIDE;
 
   virtual void UpdateExtensionBlacklist(
     const std::vector<std::string>& blacklist) OVERRIDE;
   virtual void CheckAdminBlacklist() OVERRIDE;
   virtual void CheckForUpdatesSoon() OVERRIDE;
   virtual bool GetSyncData(
       const Extension& extension, ExtensionFilter filter,
       ExtensionSyncData* extension_sync_data) const OVERRIDE;
   virtual std::vector<ExtensionSyncData> GetSyncDataList(
       ExtensionFilter filter) const OVERRIDE;
   virtual void ProcessSyncData(
       const ExtensionSyncData& extension_sync_data,
       ExtensionFilter filter) OVERRIDE;
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_TEST_EXTENSION_SERVICE_H_