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

ui/base/dragdrop/os_exchange_data_provider_factory.cc

+// 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.
+
+#include "ui/base/dragdrop/os_exchange_data_provider_factory.h"
+
+#if defined(USE_X11) && !defined(OS_CHROMEOS)
+#include "ui/base/dragdrop/os_exchange_data_provider_aurax11.h"
+#elif defined(OS_LINUX)
+#include "ui/base/dragdrop/os_exchange_data_provider_aura.h"
+#elif defined(OS_MACOSX)
+#include "ui/base/dragdrop/os_exchange_data_provider_builder_mac.h"
+#elif defined(OS_WIN)
+#include "ui/base/dragdrop/os_exchange_data_provider_win.h"
+#endif
+
+namespace ui {
+
+OSExchangeDataProviderFactory::Factory* factory_ = nullptr;
+
+// static
+void OSExchangeDataProviderFactory::SetFactory(Factory* factory) {
+  factory_ = factory;
+}
+
+//static
+OSExchangeData::Provider* OSExchangeDataProviderFactory::CreateProvider() {
+  if (factory_)
+    return factory_->BuildProvider();
+
+#if defined(USE_X11) && !defined(OS_CHROMEOS)
+  return new OSExchangeDataProviderAuraX11();
+#elif defined(OS_LINUX)
+  return new OSExchangeDataProviderAura();
+#elif defined(OS_MACOSX)
+  return ui::BuildOSExchangeDataProviderMac();
+#elif defined(OS_WIN)
+  return new OSExchangeDataProviderWin();
+#else
+#error "Unknown operating system"
+#endif
+}
+
+}  // namespace ui