Fail gracefully if profile Temp dir can not be accessed.

chrome/common/extensions/extension_file_util.h

Index: chrome/common/extensions/extension_file_util.h
diff --git a/chrome/common/extensions/extension_file_util.h b/chrome/common/extensions/extension_file_util.h
index f6a72bc968b488d2936a90cd7d54ef0f2c4a1d4f..b26b5640135e9fdc6129a13bd8bdad11eba49dc1 100644
--- a/chrome/common/extensions/extension_file_util.h
+++ b/chrome/common/extensions/extension_file_util.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -76,6 +76,12 @@ bool CheckForIllegalFilenames(const FilePath& extension_path,
 // Get a relative file path from a chrome-extension:// URL.
 FilePath ExtensionURLToRelativeFilePath(const GURL& url);
 
+// Get a path to a temp directory for unpacking an extension.
+// This is essentially PathService::Get(chrome::DIR_USER_DATA_TEMP, ...),
+// with a histogram that allows us to understand why it is failing.
+// Return an empty file path on failure.
+FilePath GetUserDataTempDir();
+
 }  // namespace extension_file_util
 
 #endif  // CHROME_COMMON_EXTENSIONS_EXTENSION_FILE_UTIL_H_