Fix heuristic triggering incremental marking.

This changes the heuristic that starts incremental marking to be based
on a more accurate heap size estimation. Pages being swept lazily can be
accounted using the live bytes counter.

R=mstarzinger@chromium.org
BUG=v8:1682

Review URL: https://chromiumcodereview.appspot.com/9674001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11004 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/incremental-marking.cc

@@ -396,7 +396,7 @@ bool IncrementalMarking::WorthActivating() {
   return !FLAG_expose_gc &&
       FLAG_incremental_marking &&
       !Serializer::enabled() &&
-      heap_->PromotedSpaceSize() > kActivationThreshold;
+      heap_->PromotedSpaceSizeOfObjects() > kActivationThreshold;
 }