Mojo C++ bindings: support mapping mojo string to WTF::String.

mojo/public/cpp/bindings/tests/variant_test_util.h

Index: mojo/public/cpp/bindings/tests/variant_test_util.h
diff --git a/mojo/public/cpp/bindings/tests/variant_test_util.h b/mojo/public/cpp/bindings/tests/variant_test_util.h
new file mode 100644
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+++ b/mojo/public/cpp/bindings/tests/variant_test_util.h
@@ -0,0 +1,32 @@
+// Copyright 2016 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 MOJO_PUBLIC_CPP_BINDINGS_TESTS_VARIANT_TEST_UTIL_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_TESTS_VARIANT_TEST_UTIL_H_
+
+#include <string.h>
+
+#include "base/logging.h"
+#include "mojo/public/cpp/bindings/interface_request.h"
+
+namespace mojo {
+namespace test {
+
+// Converts a request of Interface1 to a request of Interface0. Interface0 and
+// Interface1 are expected to be two variants of the same mojom interface.
+// In real-world use cases, users shouldn't need to worry about this. Because it
+// is rare to deal with two variants of the same interface in the same app.
+template <typename Interface0, typename Interface1>
+InterfaceRequest<Interface0> ConvertInterfaceRequest(
+    InterfaceRequest<Interface1> request) {
+  DCHECK_EQ(0, strcmp(Interface0::Name_, Interface1::Name_));
+  InterfaceRequest<Interface0> result;
+  result.Bind(request.PassMessagePipe());
+  return result;
+}
+
+}  // namespace test
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_TESTS_VARIANT_TEST_UTIL_H_