TestingPlatformSupport: register Platform instance correctly

third_party/WebKit/Source/platform/scroll/ScrollbarTestSuite.h

Index: third_party/WebKit/Source/platform/scroll/ScrollbarTestSuite.h
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarTestSuite.h b/third_party/WebKit/Source/platform/scroll/ScrollbarTestSuite.h
index 6bb469fd2122046298c088d22d70046e044c9eb7..55012b10c8dfe698465d94f66096b91612c4788d 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarTestSuite.h
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarTestSuite.h
@@ -89,14 +89,13 @@ class ScrollbarTestSuite : public testing::Test {
   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