TestingPlatformSupport: register Platform instance correctly

third_party/WebKit/Source/platform/testing/TestingPlatformSupport.h

 /*
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 19 matching lines @@
 
 #ifndef TestingPlatformSupport_h
 #define TestingPlatformSupport_h
 
 #include "platform/PlatformExport.h"
 #include "platform/WebTaskRunner.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebCompositorSupport.h"
 #include "public/platform/WebScheduler.h"
 #include "public/platform/WebThread.h"
+#include "wtf/Allocator.h"
+#include "wtf/Assertions.h"
+#include "wtf/PtrUtil.h"
 #include "wtf/Vector.h"
 #include <memory>
+#include <utility>
 
 namespace base {
 class SimpleTestTickClock;
 class TestDiscardableMemoryAllocator;
 }
 
 namespace cc {
 class OrderedSimpleTaskRunner;
 }
 
@@ skipping 48 matching lines @@
       InterventionReporter*,
       WebViewScheduler::WebViewSchedulerSettings*) override {
     return nullptr;
   }
   void suspendTimerQueue() override {}
   void resumeTimerQueue() override {}
   void addPendingNavigation(WebScheduler::NavigatingFrameType) override {}
   void removePendingNavigation(WebScheduler::NavigatingFrameType) override {}
 };
 
+// A base class to override Platform methods for testing.  You can override the
+// behavior by subclassing TestingPlatformSupport or using
+// ScopedTestingPlatformSupport (see below).
 class TestingPlatformSupport : public Platform {
   WTF_MAKE_NONCOPYABLE(TestingPlatformSupport);
 
  public:
   struct Config {
     WebCompositorSupport* compositorSupport = nullptr;
   };
 
   TestingPlatformSupport();
   explicit TestingPlatformSupport(const Config&);
@@ skipping 15 matching lines @@
   InterfaceProvider* interfaceProvider() override;
 
  protected:
   class TestingInterfaceProvider;
 
   const Config m_config;
   Platform* const m_oldPlatform;
   std::unique_ptr<TestingInterfaceProvider> m_interfaceProvider;
 };
 
+// This class adds mocked scheduler support to TestingPlatformSupport.  See also
+// ScopedTestingPlatformSupport to use this class correctly.
 class TestingPlatformSupportWithMockScheduler : public TestingPlatformSupport {
   WTF_MAKE_NONCOPYABLE(TestingPlatformSupportWithMockScheduler);
 
  public:
   TestingPlatformSupportWithMockScheduler();
   explicit TestingPlatformSupportWithMockScheduler(const Config&);
   ~TestingPlatformSupportWithMockScheduler() override;
 
   // Platform:
   WebThread* currentThread() override;
@@ skipping 26 matching lines @@
 
  protected:
   static double getTestTime();
 
   std::unique_ptr<base::SimpleTestTickClock> m_clock;
   scoped_refptr<cc::OrderedSimpleTaskRunner> m_mockTaskRunner;
   std::unique_ptr<scheduler::RendererSchedulerImpl> m_scheduler;
   std::unique_ptr<WebThread> m_thread;
 };
 
-class ScopedUnittestsEnvironmentSetup {
+// ScopedTestingPlatformSupport<MyTestingPlatformSupport> can be used to
+// override Platform::current() with MyTestingPlatformSupport, like this:
+//
+// #include "platform/testing/TestingPlatformSupport.h"
+//
+// TEST_F(SampleTest, sampleTest) {
+//   ScopedTestingPlatformSupport<MyTestingPlatformSupport> platform;
+//   ...
+//   // You can call methods of MyTestingPlatformSupport.
+//   EXPECT_TRUE(platform->myMethodIsCalled());
+//
+//   // Another instance can be nested.
+//   {
+//     // Constructor's arguments can be passed like this.
+//     Arg arg;
+//     ScopedTestingPlatformSupport<MyAnotherTestingPlatformSupport, const Arg&>
+//         another_platform(args);
+//     ...
+//   }
+//
+//   // Here the original MyTestingPlatformSupport should be restored.
+// }
+template <class T, typename... Args>
+class ScopedTestingPlatformSupport final {
+  STACK_ALLOCATED();
+
+ public:
+  explicit ScopedTestingPlatformSupport(Args&&... args) {
+    m_testingPlatformSupport = WTF::makeUnique<T>(std::forward<Args>(args)...);
+    m_originalPlatform = Platform::current();
+    DCHECK(m_originalPlatform);
+    Platform::setCurrentPlatformForTesting(m_testingPlatformSupport.get());
+  }
+  ~ScopedTestingPlatformSupport() {
+    DCHECK_EQ(m_testingPlatformSupport.get(), Platform::current());
+    m_testingPlatformSupport.reset();
+    Platform::setCurrentPlatformForTesting(m_originalPlatform);
+  }
+
+  const T* operator->() const { return m_testingPlatformSupport.get(); }
+  T* operator->() { return m_testingPlatformSupport.get(); }
+
+ private:
+  std::unique_ptr<T> m_testingPlatformSupport;
+  Platform* m_originalPlatform;
+};
+
+class ScopedUnittestsEnvironmentSetup final {
   WTF_MAKE_NONCOPYABLE(ScopedUnittestsEnvironmentSetup);
 
  public:
   ScopedUnittestsEnvironmentSetup(int argc, char** argv);
   ~ScopedUnittestsEnvironmentSetup();
 
  private:
   class DummyPlatform;
   std::unique_ptr<base::TestDiscardableMemoryAllocator>
       m_discardableMemoryAllocator;
-  std::unique_ptr<DummyPlatform> m_platform;
+  std::unique_ptr<DummyPlatform> m_dummyPlatform;
   std::unique_ptr<cc_blink::WebCompositorSupportImpl> m_compositorSupport;
   TestingPlatformSupport::Config m_testingPlatformConfig;
   std::unique_ptr<TestingPlatformSupport> m_testingPlatformSupport;
 };
 
 }  // namespace blink
 
 #endif  // TestingPlatformSupport_h