Fix build failure introduced by r10380

TBR=mstarzinger@chromium.org

Review URL: http://codereview.chromium.org/9190002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10381 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

test/cctest/test-heap.cc

@@ -1481,7 +1481,9 @@ TEST(LeakGlobalContextViaMapProto) {
 TEST(InstanceOfStubWriteBarrier) {
   if (!i::FLAG_crankshaft) return;
   i::FLAG_allow_natives_syntax = true;
+#ifdef DEBUG
   i::FLAG_verify_heap = true;
+#endif
   InitializeVM();
   v8::HandleScope outer_scope;