Always destroy CrxInstaller on the UI Thread

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 352 matching lines @@
 
   // The temp directory extension resources were unpacked to. We own this and
   // must delete it when we are done with it.
   base::FilePath temp_dir_;
 
   // The frontend we will report results back to.
   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.
-  // NOTE: we may be deleted on the file thread. To ensure the UI is deleted on
-  // the main thread we don't use a scoped_ptr here.
-  ExtensionInstallPrompt* client_;
+  scoped_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_;
 
   // 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|
@@ skipping 47 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_