Match whole path components in DevicePathToDriveLetterPath(). Add tests.

base/file_util.h

Index: base/file_util.h
diff --git a/base/file_util.h b/base/file_util.h
index 78827e986e6c5170b8d906476be19a1addddb837..384f3948427e543706c989a17efab8e9bf8b88f5 100644
--- a/base/file_util.h
+++ b/base/file_util.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -324,10 +324,17 @@ BASE_EXPORT bool IsDotDot(const FilePath& path);
 BASE_EXPORT bool NormalizeFilePath(const FilePath& path, FilePath* real_path);
 
 #if defined(OS_WIN)
-// Given an existing file in |path|, it returns in |real_path| the path
-// in the native NT format, of the form "\Device\HarddiskVolumeXX\..".
-// Returns false it it fails. Empty files cannot be resolved with this
-// function.
+
+// Given a path in NT native form ("\Device\HarddiskVolumeXX\..."),
+// return in |drive_letter_path| the equivalent path that starts with
+// a drive letter ("C:\...").  Return false if no such path exists.
+BASE_EXPORT bool DevicePathToDriveLetterPath(const FilePath& device_path,
+                                             FilePath* drive_letter_path);
+
+// Given an existing file in |path|, set |real_path| to the path
+// in native NT format, of the form "\Device\HarddiskVolumeXX\..".
+// Returns false if the path can not be found. Empty files cannot
+// be resolved with this function.
 BASE_EXPORT bool NormalizeToNativeFilePath(const FilePath& path,
                                            FilePath* nt_path);
 #endif