Add support for tracking down leak of the hole value.

src/api.h

 // Copyright 2008 the V8 project authors. 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
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 226 matching lines @@
 
 template <class T>
 v8::internal::Handle<T> v8::internal::Handle<T>::EscapeFrom(
     v8::HandleScope* scope) {
   return Utils::OpenHandle(*scope->Close(Utils::ToLocal(*this)));
 }
 
 
 // Implementations of ToLocal
 
-#define MAKE_TO_LOCAL(Name, From, To) \
+#define MAKE_TO_LOCAL(Name, From, To)                                       \
   Local<v8::To> Utils::Name(v8::internal::Handle<v8::internal::From> obj) { \
-    return Local<To>(reinterpret_cast<To*>(obj.location())); \
+    ASSERT(!obj->IsTheHole());                                              \
+    return Local<To>(reinterpret_cast<To*>(obj.location()));                \
   }
 
 MAKE_TO_LOCAL(ToLocal, Context, Context)
 MAKE_TO_LOCAL(ToLocal, Object, Value)
 MAKE_TO_LOCAL(ToLocal, JSFunction, Function)
 MAKE_TO_LOCAL(ToLocal, String, String)
 MAKE_TO_LOCAL(ToLocal, JSObject, Object)
 MAKE_TO_LOCAL(ToLocal, JSArray, Array)
 MAKE_TO_LOCAL(ToLocal, Proxy, External)
 MAKE_TO_LOCAL(ToLocal, FunctionTemplateInfo, FunctionTemplate)
@@ skipping 185 matching lines @@
 #ifdef DEBUG
   v8::ImplementationUtilities::ZapHandleRange(
       reinterpret_cast<void**>(spare),
       reinterpret_cast<void**>(&spare[kHandleBlockSize]));
 #endif
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_API_H_