Refactor build target for sync

sync/protocol/sync_proto_export.h

Index: sync/protocol/sync_proto_export.h
diff --git a/sync/protocol/sync_proto_export.h b/sync/protocol/sync_proto_export.h
new file mode 100644
index 0000000000000000000000000000000000000000..15b5b49cf8890c3e2ef7fbecfcd77144c4a75ace
--- /dev/null
+++ b/sync/protocol/sync_proto_export.h
@@ -0,0 +1,29 @@
+// Copyright (c) 2014 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 SYNC_PROTOCOL_SYNC_PROTO_EXPORT_H_
+#define SYNC_PROTOCOL_SYNC_PROTO_EXPORT_H_
+
+#if defined(COMPONENT_BUILD)
+#if defined(WIN32)
+
+#if defined(SYNC_PROTO_IMPLEMENTATION)
+#define SYNC_PROTO_EXPORT __declspec(dllexport)
+#else
+#define SYNC_PROTO_EXPORT __declspec(dllimport)
+#endif  // defined(SYNC_PROTO_IMPLEMENTATION)
+
+#else  // defined(WIN32)
+#if defined(SYNC_PROTO_IMPLEMENTATION)
+#define SYNC_PROTO_EXPORT __attribute__((visibility("default")))
+#else
+#define SYNC_PROTO_EXPORT
+#endif  // defined(SYNC_IMPLEMENTATION)
+#endif
+
+#else  // defined(COMPONENT_BUILD)
+#define SYNC_PROTO_EXPORT
+#endif
+
+#endif  // SYNC_PROTOCOL_SYNC_PROTO_EXPORT_H_