TestingPlatformSupport: register Platform instance correctly

third_party/WebKit/Source/platform/scroll/ScrollbarTestSuite.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 ScrollbarTestSuite_h
 #define ScrollbarTestSuite_h
 
 #include "platform/heap/GarbageCollected.h"
 #include "platform/scroll/ScrollableArea.h"
 #include "platform/scroll/Scrollbar.h"
@@ skipping 71 matching lines @@
   ScrollOffset m_maximumScrollOffset;
 };
 
 class ScrollbarTestSuite : public testing::Test {
  public:
   ScrollbarTestSuite() {}
 
   void SetUp() override {
     TestingPlatformSupport::Config config;
     config.compositorSupport = Platform::current()->compositorSupport();
-    m_fakePlatform =
-        WTF::makeUnique<TestingPlatformSupportWithMockScheduler>(config);
+    m_fakePlatform.reset(
+        WTF::makeUnique<TestingPlatformSupportWithMockScheduler>(config));
   }
 
-  void TearDown() override { m_fakePlatform = nullptr; }
-
  private:
-  std::unique_ptr<TestingPlatformSupportWithMockScheduler> m_fakePlatform;
+  ScopedTestingPlatformSupport<TestingPlatformSupportWithMockScheduler>
+      m_fakePlatform;
 };
 
 }  // namespace blink
 
 #endif