Don't NULL-check GlobalHandle::Node::object_

src/global-handles.cc

Index: src/global-handles.cc
diff --git a/src/global-handles.cc b/src/global-handles.cc
index f9c4a4f580213f833f2833b07ad74459cd32a6a8..4a7292547f1c06b6c180bf09671abfd1492f143e 100644
--- a/src/global-handles.cc
+++ b/src/global-handles.cc
@@ -78,6 +78,7 @@ class GlobalHandles::Node {
 #endif
 
   void Initialize(int index, Node** first_free) {
+    object_ = reinterpret_cast<Object*>(kGlobalHandleZapValue);

[vogelheim, 2016/01/25 12:00:19]

nitpick: Wouldn't it be better for debugging to distinguish the "not
initialized" guard value from the "already dead" value? I.e., introduce a
kGlobalHandleUninitialized?

(Not sure if worth the hassle, though.)

[jochen (gone - plz use gerrit), 2016/01/25 13:05:48]

since we recycle handles, they're expected to constantly go back and forth
between zapped and valid

     index_ = static_cast<uint8_t>(index);
     DCHECK(static_cast<int>(index_) == index);
     set_state(FREE);
@@ -250,9 +251,9 @@ class GlobalHandles::Node {
   }
 
   void MakeWeak(void* parameter, WeakCallback weak_callback) {
-    DCHECK(weak_callback != NULL);
+    DCHECK(weak_callback != nullptr);
     DCHECK(IsInUse());
-    CHECK(object_ != NULL);
+    CHECK_NE(object_, reinterpret_cast<Object*>(kGlobalHandleZapValue));
     set_state(WEAK);
     set_weakness_type(NORMAL_WEAK);
     set_parameter(parameter);
@@ -264,7 +265,7 @@ class GlobalHandles::Node {
                 v8::WeakCallbackType type) {
     DCHECK(phantom_callback != nullptr);
     DCHECK(IsInUse());
-    CHECK(object_ != nullptr);
+    CHECK_NE(object_, reinterpret_cast<Object*>(kGlobalHandleZapValue));
     set_state(WEAK);
     switch (type) {
       case v8::WeakCallbackType::kParameter: