Oilpan: GC_TRACING: Improve object path dump

Source/platform/heap/Handle.h

Index: Source/platform/heap/Handle.h
diff --git a/Source/platform/heap/Handle.h b/Source/platform/heap/Handle.h
index 6de5dbc17563d21e82f0fec9aadefca5d49d8e44..4c63c1cfcefb23109ebd82f76d99210672b7a679 100644
--- a/Source/platform/heap/Handle.h
+++ b/Source/platform/heap/Handle.h
@@ -287,30 +287,32 @@ class Persistent : public PersistentBase<RootsAccessor, Persistent<T, RootsAcces
     WTF_DISALLOW_CONSTRUCTION_FROM_ZERO(Persistent);
     WTF_DISALLOW_ZERO_ASSIGNMENT(Persistent);
 public:
-    Persistent() : m_raw(0) { }
+    Persistent() : m_raw(0) { recordBacktrace(); }

[haraken, 2014/06/16 01:15:40]

I'm not sure if you want to record a backtrace for a null persistent.

 
-    Persistent(std::nullptr_t) : m_raw(0) { }
+    Persistent(std::nullptr_t) : m_raw(0) { recordBacktrace(); }

[haraken, 2014/06/16 01:15:40]

Ditto.

 
     Persistent(T* raw) : m_raw(raw)
     {
         ASSERT_IS_VALID_PERSISTENT_POINTER(m_raw);
+        recordBacktrace();
     }
 
     explicit Persistent(T& raw) : m_raw(&raw)
     {
         ASSERT_IS_VALID_PERSISTENT_POINTER(m_raw);
+        recordBacktrace();
     }
 
-    Persistent(const Persistent& other) : m_raw(other) { }
+    Persistent(const Persistent& other) : m_raw(other) { recordBacktrace(); }
 
     template<typename U>
-    Persistent(const Persistent<U, RootsAccessor>& other) : m_raw(other) { }
+    Persistent(const Persistent<U, RootsAccessor>& other) : m_raw(other) { recordBacktrace(); }
 
     template<typename U>
-    Persistent(const Member<U>& other) : m_raw(other) { }
+    Persistent(const Member<U>& other) : m_raw(other) { recordBacktrace(); }
 
     template<typename U>
-    Persistent(const RawPtr<U>& other) : m_raw(other.get()) { }
+    Persistent(const RawPtr<U>& other) : m_raw(other.get()) { recordBacktrace(); }
 
     template<typename U>
     Persistent& operator=(U* other)
@@ -342,7 +344,7 @@ public:
     {
         COMPILE_ASSERT_IS_GARBAGE_COLLECTED(T, NonGarbageCollectedObjectInPersistent);
 #if ENABLE(GC_TRACING)
-        visitor->setHostInfo(this, "Persistent");
+        visitor->setHostInfo(this, m_tracingName.isEmpty() ? "Persistent" : m_tracingName);

[haraken, 2014/06/16 01:15:40]

Just help me understand: In what situation can the m_tracingName be empty?

[tkent, 2014/06/16 02:34:47]

When we forget to add recordBacktrace() :-)

 #endif
         visitor->mark(m_raw);
     }
@@ -393,6 +395,16 @@ public:
     T* get() const { return m_raw; }
 
 private:
+#if ENABLE(GC_TRACING)
+    void recordBacktrace()
+    {
+        m_tracingName = Heap::createBacktraceString();
+    }
+
+    String m_tracingName;
+#else
+    inline void recordBacktrace() { }
+#endif
     T* m_raw;
 
     friend class CrossThreadPersistent<T>;
@@ -425,7 +437,13 @@ public:
     template<typename OtherCollection>
     PersistentHeapCollectionBase(const OtherCollection& other) : Collection(other) { }
 
-    void trace(Visitor* visitor) { visitor->trace(*static_cast<Collection*>(this)); }
+    void trace(Visitor* visitor)
+    {
+#if ENABLE(GC_TRACING)
+        visitor->setHostInfo(this, "PersistentHeapCollectionBase");
+#endif
+        visitor->trace(*static_cast<Collection*>(this));
+    }
 };
 
 template<