Allow OSExchangeData::Provider to be overridden at run time.

ui/base/dragdrop/os_exchange_data_provider_builder_mac.h

Index: ui/base/dragdrop/os_exchange_data_provider_builder_mac.h
diff --git a/ui/base/dragdrop/os_exchange_data_provider_builder_mac.h b/ui/base/dragdrop/os_exchange_data_provider_builder_mac.h
new file mode 100644
index 0000000000000000000000000000000000000000..14351be46b5044900f8c046edabd1f1e9f7f9ebe
--- /dev/null
+++ b/ui/base/dragdrop/os_exchange_data_provider_builder_mac.h
@@ -0,0 +1,20 @@
+// 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 UI_BASE_DRAGDROP_OS_EXCHANGE_DATA_PROVIDER_BUILDER_MAC_H_
+#define UI_BASE_DRAGDROP_OS_EXCHANGE_DATA_PROVIDER_BUILDER_MAC_H_
+
+#include <memory>
+
+#include "ui/base/dragdrop/os_exchange_data.h"
+
+namespace ui {
+
+// We can't include os_exchange_data_provider_mac.h from arbitrary C++ files
+// because it depends on the Objective-C headers.
+std::unique_ptr<OSExchangeData::Provider> BuildOSExchangeDataProviderMac();
+
+}  // namespace ui
+
+#endif  // UI_BASE_DRAGDROP_OS_EXCHANGE_DATA_PROVIDER_BUILDER_MAC_H_