[views-mus] Prevent creating a native OzonePlatform in mus tests.

ui/base/dragdrop/os_exchange_data_provider_factory.h

 // 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_FACTORY_H_
 #define UI_BASE_DRAGDROP_OS_EXCHANGE_DATA_PROVIDER_FACTORY_H_
 
 #include <memory>
 
 #include "ui/base/dragdrop/os_exchange_data.h"
 #include "ui/base/ui_base_export.h"
 
 namespace ui {
 
 // Builds OSExchangeDataProviders. We need to be able to switch providers at
 // runtime based on the configuration flags. If no factory is set,
 // CreateProvider() will default to the current operating system's default.
 class UI_BASE_EXPORT OSExchangeDataProviderFactory {
  public:
   class Factory {
    public:
     virtual std::unique_ptr<OSExchangeData::Provider> BuildProvider() = 0;
   };
 
   // Sets the factory which builds the providers.
   static void SetFactory(Factory* factory);
 
+  // Returns the current factory and sets the factory to null.
+  static Factory* TakeFactory();

[sky, 2017/04/12 19:38:15]

Can this return a std::unique_ptr?

[Elliot Glaysher, 2017/04/12 19:52:25]

Not easily without changing the ownership the Factory, which in all cases I know
about is an object with its own ownership semantics.

+
   // Creates a Provider based on the current configuration.
   static std::unique_ptr<OSExchangeData::Provider> CreateProvider();
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_DRAGDROP_OS_EXCHANGE_DATA_PROVIDER_FACTORY_H_