Introduce a handle zapping setting, and enable it by default for release and debug

src/handles.cc

Index: src/handles.cc
diff --git a/src/handles.cc b/src/handles.cc
index fc45aaa8b6e0169b70672fd2dfde691813a66849..fdfc01a425df5280028db9fffaf83295b985c19d 100644
--- a/src/handles.cc
+++ b/src/handles.cc
@@ -101,7 +101,7 @@ void HandleScope::DeleteExtensions(Isolate* isolate) {
 }
 
 
-#ifdef ENABLE_EXTRA_CHECKS
+#ifdef ENABLE_HANDLE_ZAPPING
 void HandleScope::ZapRange(Object** start, Object** end) {
   ASSERT(end - start <= kHandleBlockSize);
   for (Object** p = start; p != end; p++) {
@@ -554,7 +554,7 @@ v8::Handle<v8::Array> GetKeysForNamedInterceptor(Handle<JSReceiver> receiver,
     LOG(isolate, ApiObjectAccess("interceptor-named-enum", *object));
     result = args.Call(enum_fun);
   }
-#if ENABLE_EXTRA_CHECKS
+#if ENABLE_HANDLE_ZAPPING
   CHECK(result.IsEmpty() || v8::Utils::OpenHandle(*result)->IsJSObject());
 #endif
   return v8::Local<v8::Array>::New(reinterpret_cast<v8::Isolate*>(isolate),
@@ -575,7 +575,7 @@ v8::Handle<v8::Array> GetKeysForIndexedInterceptor(Handle<JSReceiver> receiver,
         v8::ToCData<v8::IndexedPropertyEnumerator>(interceptor->enumerator());
     LOG(isolate, ApiObjectAccess("interceptor-indexed-enum", *object));
     result = args.Call(enum_fun);
-#if ENABLE_EXTRA_CHECKS
+#if ENABLE_HANDLE_ZAPPING
     CHECK(result.IsEmpty() || v8::Utils::OpenHandle(*result)->IsJSObject());
 #endif
   }