Disable incremental marking when GC extension is exposed.

R=erik.corry@gmail.com

Review URL: http://codereview.chromium.org/8366001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9737 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/incremental-marking.cc

@@ -354,7 +354,8 @@ bool IncrementalMarking::WorthActivating() {
   static const intptr_t kActivationThreshold = 0;
 #endif
 
-  return FLAG_incremental_marking &&
+  return !FLAG_expose_gc &&
+      FLAG_incremental_marking &&
       !Serializer::enabled() &&
       heap_->PromotedSpaceSize() > kActivationThreshold;
 }