Add ShellIntegration::ActivateMetroChrome, which launches Chrome in metro-mode on Windows 8.

base/win/metro_exports.cc

Index: base/win/metro_exports.cc
diff --git a/base/win/metro_exports.cc b/base/win/metro_exports.cc
new file mode 100644
index 0000000000000000000000000000000000000000..4a6be7985158b811fc57f37141b8b3517ba98ef1
--- /dev/null
+++ b/base/win/metro_exports.cc
@@ -0,0 +1,11 @@
+// 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/win/metro_exports.h"
+
+namespace metro_exports {
+
+const char kActivateApplication[] = "ActivateApplication";
+
+}  // namespace metro_exports