Allow incremental marking when expose_gc is turned on.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 976d65e959fdc35e50a8efe8964ff9e00a1388c4..49ab6564dac09bf8758a55a2ef865322a7c4c121 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -5322,8 +5322,7 @@ bool Heap::IdleNotification(int hint) {
       AgeInlineCaches();
     }
     int mark_sweep_time = Min(TimeMarkSweepWouldTakeInMs(), 1000);
-    if (hint >= mark_sweep_time && !FLAG_expose_gc &&
-        incremental_marking()->IsStopped()) {
+    if (hint >= mark_sweep_time && incremental_marking()->IsStopped()) {
       HistogramTimerScope scope(isolate_->counters()->gc_context());
       CollectAllGarbage(kReduceMemoryFootprintMask,
                         "idle notification: contexts disposed");
@@ -5342,7 +5341,7 @@ bool Heap::IdleNotification(int hint) {
     return false;
   }
 
-  if (!FLAG_incremental_marking || FLAG_expose_gc || Serializer::enabled()) {
+  if (!FLAG_incremental_marking || Serializer::enabled()) {
     return IdleGlobalGC();
   }