Fix compile.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index f054e2cc98710ef08ed856f389d83a73cdd2e9d4..088afc9502acab36b7df5e8853b2d9041de6d185 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -4477,8 +4477,9 @@ bool Heap::IdleNotification(int hint) {
 
   // If the IdleNotifcation is called with a large hint we will wait for
   // the sweepter threads here.
-  if (hint >= kMinHintForFullGC && IsConcurrentSweepingInProgress()) {
-    WaitUntilSweepingCompleted();
+  if (hint >= kMinHintForFullGC &&
+      mark_compact_collector()->IsConcurrentSweepingInProgress()) {
+    mark_compact_collector()->WaitUntilSweepingCompleted();
   }
 
   return false;