Reland: mash: Fix MusPropertyMirrorAsh for owned properties; add test.

ash/public/cpp/ash_public_export.h

Index: ash/public/cpp/ash_public_export.h
diff --git a/ash/public/cpp/ash_public_export.h b/ash/public/cpp/ash_public_export.h
new file mode 100644
index 0000000000000000000000000000000000000000..810843464b6f0975cc0fc792937a8692509d3e79
--- /dev/null
+++ b/ash/public/cpp/ash_public_export.h
@@ -0,0 +1,34 @@
+// Copyright 2017 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 ASH_PUBLIC_CPP_ASH_PUBLIC_EXPORT_H_
+#define ASH_PUBLIC_CPP_ASH_PUBLIC_EXPORT_H_
+
+#if defined(COMPONENT_BUILD)
+
+#if defined(WIN32)
+
+#if defined(ASH_PUBLIC_IMPLEMENTATION)
+#define ASH_PUBLIC_EXPORT __declspec(dllexport)
+#else
+#define ASH_PUBLIC_EXPORT __declspec(dllimport)
+#endif
+
+#else  // !defined(WIN32)
+
+#if defined(ASH_PUBLIC_IMPLEMENTATION)
+#define ASH_PUBLIC_EXPORT __attribute((visibility("default")))
+#else
+#define ASH_PUBLIC_EXPORT
+#endif
+
+#endif  // defined(WIN32)
+
+#else  // !defined(COMPONENT_BUILD)
+
+#define ASH_PUBLIC_EXPORT
+
+#endif  // defined(COMPONENT_BUILD)
+
+#endif  // ASH_PUBLIC_CPP_ASH_PUBLIC_EXPORT_H_