GC plugin: remove mixin trace override restriction.

third_party/WebKit/Source/platform/heap/HeapTest.cpp

 /*
  * Copyright (C) 2013 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 4550 matching lines @@
     destructorsCalledOnGC<HeapHashSet<RefPtr<RefCountedWithDestructor>>>(true);
     destructorsCalledOnGC<HeapListHashSet<RefPtr<RefCountedWithDestructor>>>(true);
     destructorsCalledOnGC<HeapLinkedHashSet<RefPtr<RefCountedWithDestructor>>>(true);
 }
 
 class MixinA : public GarbageCollectedMixin {
 public:
     MixinA() : m_obj(IntWrapper::create(100)) { }
     DEFINE_INLINE_VIRTUAL_TRACE()
     {
+        s_traceCount++;
         visitor->trace(m_obj);
     }
+
+    static int s_traceCount;
+
     Member<IntWrapper> m_obj;
 };
 
+int MixinA::s_traceCount = 0;
+
 class MixinB : public GarbageCollectedMixin {
 public:
     MixinB() : m_obj(IntWrapper::create(101)) { }
     DEFINE_INLINE_VIRTUAL_TRACE()
     {
         visitor->trace(m_obj);
     }
     Member<IntWrapper> m_obj;
 };
 
@@ skipping 70 matching lines @@
     {
         Persistent<MixinB> b = obj;
         preciselyCollectGarbage();
         EXPECT_EQ(0, IntWrapper::s_destructorCalls);
         EXPECT_EQ(2, DerivedMultipleMixins::s_traceCalled);
     }
     preciselyCollectGarbage();
     EXPECT_EQ(4, IntWrapper::s_destructorCalls);
 }
 
+class MixinInstanceWithoutTrace : public GarbageCollected<MixinInstanceWithoutTrace>, public MixinA {
+    USING_GARBAGE_COLLECTED_MIXIN(MixinInstanceWithoutTrace);
+public:
+    MixinInstanceWithoutTrace()
+    {
+    }
+};
+
+TEST(HeapTest, MixinInstanceWithoutTrace)
+{
+    // Verify that a mixin instance without any traceable
+    // references inherits the mixin's trace implementation.
+    clearOutOldGarbage();
+    MixinA::s_traceCount = 0;
+    MixinInstanceWithoutTrace* obj = new MixinInstanceWithoutTrace();
+    {
+        Persistent<MixinA> a = obj;
+        preciselyCollectGarbage();
+        EXPECT_EQ(1, MixinA::s_traceCount);
+    }
+    {
+        Persistent<MixinInstanceWithoutTrace> b = obj;
+        preciselyCollectGarbage();
+        EXPECT_EQ(2, MixinA::s_traceCount);
+    }
+    preciselyCollectGarbage();
+    EXPECT_EQ(2, MixinA::s_traceCount);
+}
+
 class GCParkingThreadTester {
 public:
     static void test()
     {
         OwnPtr<WebThread> sleepingThread = adoptPtr(Platform::current()->createThread("SleepingThread"));
         sleepingThread->taskRunner()->postTask(BLINK_FROM_HERE, new Task(threadSafeBind(sleeperMainFunc)));
 
         // Wait for the sleeper to run.
         while (!s_sleeperRunning) {
             Platform::current()->yieldCurrentThread();
@@ skipping 1814 matching lines @@
     EXPECT_EQ(1u, vector2.size());
 // TODO(Oilpan): when Vector.h's contiguous container support no longer disables
 // Vector<>s with inline capacity, remove.
 #if !defined(ANNOTATE_CONTIGUOUS_CONTAINER)
     EXPECT_EQ(16u, vector1.capacity());
     EXPECT_EQ(16u, vector2.capacity());
 #endif
 }
 
 } // namespace blink