Use PreloadCheckGroup in ExtensionInstallChecker. Make RequirementsChecker a PreloadCheck.

chrome/browser/extensions/crx_installer.h

 // Copyright (c) 2012 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_CRX_INSTALLER_H_
 #define CHROME_BROWSER_EXTENSIONS_CRX_INSTALLER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 184 matching lines @@
     set_install_flag(kInstallFlagInstallImmediately, val);
   }
   void set_do_not_sync(bool val) {
     set_install_flag(kInstallFlagDoNotSync, val);
   }
 
   bool did_handle_successfully() const { return did_handle_successfully_; }
 
   Profile* profile() { return install_checker_.profile(); }
 
-  const Extension* extension() { return install_checker_.extension().get(); }
+  const Extension* extension() { return extension_.get(); }
 
   // The currently installed version of the extension, for updates. Will be
   // invalid if this isn't an update.
   const base::Version& current_version() const { return current_version_; }
 
  private:
   friend class ::ExtensionServiceTest;
   friend class ExtensionUpdaterTest;
   friend class ExtensionCrxInstallerTest;
 
@@ skipping 157 matching lines @@
   base::WeakPtr<ExtensionService> service_weak_;
 
   // The client we will work with to do the installation. This can be NULL, in
   // which case the install is silent.
   std::unique_ptr<ExtensionInstallPrompt> client_;
 
   // The root of the unpacked extension directory. This is a subdirectory of
   // temp_dir_, so we don't have to delete it explicitly.
   base::FilePath unpacked_extension_root_;
 
+  // The extension being installed.
+  scoped_refptr<const Extension> extension_;
+
   // True when the CRX being installed was just downloaded.
   // Used to trigger extra checks before installing.
   bool apps_require_extension_mime_type_;
 
   // Allows for the possibility of a normal install (one in which a |client|
   // is provided in the ctor) to proceed without showing the permissions prompt
   // dialog.
   bool allow_silent_install_;
 
   // Allows for the possibility of an installation without granting any
@@ skipping 42 matching lines @@
 
   // Performs requirements, policy and blacklist checks on the extension.
   ExtensionInstallChecker install_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(CrxInstaller);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_CRX_INSTALLER_H_