Oilpan: Fix isAlive dispatching for GarbageCollectedMixins.

Source/heap/HeapTest.cpp

Index: Source/heap/HeapTest.cpp
diff --git a/Source/heap/HeapTest.cpp b/Source/heap/HeapTest.cpp
index 5b9d450b0cd2ca77736bf2debacb03f96b544d09..d862b8a43ee47d93f2c39b3c3f9d0159dc163023 100644
--- a/Source/heap/HeapTest.cpp
+++ b/Source/heap/HeapTest.cpp
@@ -175,6 +175,7 @@ public:
     static SimpleObject* create() { return new SimpleObject(); }
     void trace(Visitor*) { }
     char getPayload(int i) { return payload[i]; }
+    virtual void virtualMethod() { }

[Mads Ager (chromium), 2014/04/02 18:13:56]

I'll add a comment that this make sure that the object has a vtable which means
that adjustment becomes needed when a mixin is added in the inheritance
hierarchy.

 protected:
     SimpleObject() { }
     char payload[64];
@@ -1137,10 +1138,9 @@ class Mixin : public GarbageCollectedMixin {
 public:
     virtual void trace(Visitor* visitor) { }
 
-    char getPayload(int i) { return m_padding[i]; }
+    virtual char getPayload(int i) { return m_padding[i]; }
 
 protected:
-    // This is to force ptr diff for SimpleObject, Mixin, and UseMixin.
     int m_padding[8];
 };
 
@@ -2983,20 +2983,25 @@ TEST(HeapTest, CollectionNesting)
     EXPECT_EQ(1, IntWrapper::s_destructorCalls);
 }
 
-TEST(heap, GarbageCollectedMixin)
+TEST(HeapTest, GarbageCollectedMixin)
 {
     HeapStats initialHeapStats;
     clearOutOldGarbage(&initialHeapStats);
 
     Persistent<UseMixin> usemixin = UseMixin::create();
-    ASSERT_EQ(0, UseMixin::s_traceCount);
+    EXPECT_EQ(0, UseMixin::s_traceCount);
     Heap::collectGarbage(ThreadState::NoHeapPointersOnStack);
-    ASSERT_EQ(1, UseMixin::s_traceCount);
+    EXPECT_EQ(1, UseMixin::s_traceCount);
 
     Persistent<Mixin> mixin = usemixin;
     usemixin = nullptr;
     Heap::collectGarbage(ThreadState::NoHeapPointersOnStack);
-    ASSERT_EQ(2, UseMixin::s_traceCount);
+    EXPECT_EQ(2, UseMixin::s_traceCount);
+
+    PersistentHeapHashSet<WeakMember<Mixin> > weakMap;
+    weakMap.add(UseMixin::create());
+    Heap::collectGarbage(ThreadState::NoHeapPointersOnStack);
+    EXPECT_EQ(0u, weakMap.size());
 }
 
 TEST(HeapTest, CollectionNesting2)