Make base compile with no "using base::FilePath".

base/file_path.cc

 // 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.
 
 #include "base/file_path.h"
 
 #include <string.h>
 #include <algorithm>
 
 #include "base/basictypes.h"
@@ skipping 11 matching lines @@
 #include "base/mac/scoped_cftyperef.h"
 #include "base/third_party/icu/icu_utf.h"
 #endif
 
 #if defined(OS_WIN)
 #include <windows.h>
 #elif defined(OS_MACOSX)
 #include <CoreFoundation/CoreFoundation.h>
 #endif
 
+namespace base {
+
 #if defined(FILE_PATH_USES_WIN_SEPARATORS)
 const FilePath::CharType FilePath::kSeparators[] = FILE_PATH_LITERAL("\\/");
 #else  // FILE_PATH_USES_WIN_SEPARATORS
 const FilePath::CharType FilePath::kSeparators[] = FILE_PATH_LITERAL("/");
 #endif  // FILE_PATH_USES_WIN_SEPARATORS
 
 const FilePath::CharType FilePath::kCurrentDirectory[] = FILE_PATH_LITERAL(".");
 const FilePath::CharType FilePath::kParentDirectory[] = FILE_PATH_LITERAL("..");
 
 const FilePath::CharType FilePath::kExtensionSeparator = FILE_PATH_LITERAL('.');
@@ skipping 1205 matching lines @@
   }
   return FilePath(copy);
 #else
   return *this;
 #endif
 }
 
 void PrintTo(const FilePath& path, std::ostream* out) {
   *out << path.value();
 }
+
+}  // namespace base