[Oilpan] Add use-after-free detector in Member<>

third_party/WebKit/Source/platform/heap/Handle.h

Index: third_party/WebKit/Source/platform/heap/Handle.h
diff --git a/third_party/WebKit/Source/platform/heap/Handle.h b/third_party/WebKit/Source/platform/heap/Handle.h
index 64e43fd71243011277fb2052e26dfe146148b0dc..e33c29f6a44e1ae4f552a3fde811d11bbc6e7579 100644
--- a/third_party/WebKit/Source/platform/heap/Handle.h
+++ b/third_party/WebKit/Source/platform/heap/Handle.h
@@ -771,10 +771,30 @@ public:
         checkPointer();
     }
 
-    T* get() const { return m_raw; }
+    T* get() const
+    {
+#if ENABLE(ASSERT)
+        // Verify that this handle points to a live on-heap object, if a pointer
+        // has been assigned to this handle out of GarbageCollectedMixin constructions.
+        if (m_raw && m_gcGeneration) {
+            ASSERT(m_gcGeneration == GarbageCollectedMixinTrait<T>::heapObjectHeader(m_raw)->gcGeneration());
+        }
+#endif
+        return m_raw;
+    }
 
-    void clear() { m_raw = nullptr; }
+    // This method is an accessor without any security checks, and it is
+    // expected to be used under some limited condition.
+    // So do NOT use it, if you do not know what it means.
+    T* unsafeGet() const
+    {
+        return m_raw;
+    }
 
+    void clear()
+    {
+        m_raw = nullptr;
+    }
 
 protected:
     void checkPointer()
@@ -799,16 +819,18 @@ protected:
         // but we cannot call it here because it requires to include T.h.
         // So we currently only try to implement the check for (a), but do
         // not insist that T's definition is in scope.
-        if (IsFullyDefined<T>::value && !IsGarbageCollectedMixin<T>::value)
-            ASSERT(HeapObjectHeader::fromPayload(m_raw)->checkHeader());
+        m_gcGeneration = GarbageCollectedMixinTrait<T>::gcGeneration(m_raw);
 #endif
     }
 
     T* m_raw;
 
+#if ENABLE(ASSERT)
+    uint32_t m_gcGeneration;
+#endif
+
     template<bool x, WTF::WeakHandlingFlag y, WTF::ShouldWeakPointersBeMarkedStrongly z, typename U, typename V> friend struct CollectionBackingTraceTrait;
     friend class Visitor;
-
 };
 
 // WeakMember is similar to Member in that it is used to point to other oilpan
@@ -872,6 +894,12 @@ public:
         return *this;
     }
 
+    T* get() const
+    {
+        // WeakMember may point to a dead object, so we skip the verification.
+        return Member<T>::unsafeGet();
+    }
+
 private:
     T** cell() const { return const_cast<T**>(&this->m_raw); }
 
@@ -946,15 +974,15 @@ public:
 };
 
 // Comparison operators between (Weak)Members, Persistents, and UntracedMembers.
-template<typename T, typename U> inline bool operator==(const Member<T>& a, const Member<U>& b) { return a.get() == b.get(); }
-template<typename T, typename U> inline bool operator!=(const Member<T>& a, const Member<U>& b) { return a.get() != b.get(); }
+template<typename T, typename U> inline bool operator==(const Member<T>& a, const Member<U>& b) { return a.unsafeGet() == b.unsafeGet(); }
+template<typename T, typename U> inline bool operator!=(const Member<T>& a, const Member<U>& b) { return a.unsafeGet() != b.unsafeGet(); }
 template<typename T, typename U> inline bool operator==(const Persistent<T>& a, const Persistent<U>& b) { return a.get() == b.get(); }
 template<typename T, typename U> inline bool operator!=(const Persistent<T>& a, const Persistent<U>& b) { return a.get() != b.get(); }
 
-template<typename T, typename U> inline bool operator==(const Member<T>& a, const Persistent<U>& b) { return a.get() == b.get(); }
-template<typename T, typename U> inline bool operator!=(const Member<T>& a, const Persistent<U>& b) { return a.get() != b.get(); }
-template<typename T, typename U> inline bool operator==(const Persistent<T>& a, const Member<U>& b) { return a.get() == b.get(); }
-template<typename T, typename U> inline bool operator!=(const Persistent<T>& a, const Member<U>& b) { return a.get() != b.get(); }
+template<typename T, typename U> inline bool operator==(const Member<T>& a, const Persistent<U>& b) { return a.unsafeGet() == b.get(); }
+template<typename T, typename U> inline bool operator!=(const Member<T>& a, const Persistent<U>& b) { return a.unsafeGet() != b.get(); }
+template<typename T, typename U> inline bool operator==(const Persistent<T>& a, const Member<U>& b) { return a.get() == b.unsafeGet(); }
+template<typename T, typename U> inline bool operator!=(const Persistent<T>& a, const Member<U>& b) { return a.get() != b.unsafeGet(); }
 
 template<typename T>
 class DummyBase {
@@ -1414,11 +1442,9 @@ template<typename T> struct PtrHash<blink::Member<T>> : PtrHash<T*> {
     static bool equal(const U& a, const V& b) { return a == b; }
 };
 
-template<typename T> struct PtrHash<blink::WeakMember<T>> : PtrHash<blink::Member<T>> {
-};
+template<typename T> struct PtrHash<blink::WeakMember<T>> : PtrHash<blink::Member<T>> { };
 
-template<typename T> struct PtrHash<blink::UntracedMember<T>> : PtrHash<blink::Member<T>> {
-};
+template<typename T> struct PtrHash<blink::UntracedMember<T>> : PtrHash<blink::Member<T>> { };
 
 // PtrHash is the default hash for hash tables with members.
 template<typename T> struct DefaultHash<blink::Member<T>> {