Introduce Platform::setCurrentPlatformForTesting

third_party/WebKit/Source/platform/scroll/ScrollableAreaTest.cpp

Index: third_party/WebKit/Source/platform/scroll/ScrollableAreaTest.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollableAreaTest.cpp b/third_party/WebKit/Source/platform/scroll/ScrollableAreaTest.cpp
index 4633bc4af8467013c9e5c4e428bab270a42f4ce9..ee962d9a767b5e24094048fbf2bae84d5d69160b 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollableAreaTest.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollableAreaTest.cpp
@@ -75,26 +75,22 @@ private:
 
 class ScrollableAreaTest : public testing::Test {
 public:
-    ScrollableAreaTest() : m_oldPlatform(nullptr) { }
+    ScrollableAreaTest() { }
 
     void SetUp() override
     {
-        m_oldPlatform = Platform::current();
         TestingPlatformSupport::Config config;
-        config.compositorSupport = m_oldPlatform->compositorSupport();
+        config.compositorSupport = Platform::current()->compositorSupport();
         m_fakePlatform = adoptPtr(new TestingPlatformSupportWithMockScheduler(config));
-        Platform::initialize(m_fakePlatform.get());
     }
 
     void TearDown() override
     {
-        Platform::initialize(m_oldPlatform);
         m_fakePlatform = nullptr;
     }
 
 private:
     OwnPtr<TestingPlatformSupportWithMockScheduler> m_fakePlatform;
-    Platform* m_oldPlatform; // Not owned.
 };
 
 TEST_F(ScrollableAreaTest, ScrollAnimatorCurrentPositionShouldBeSync)