Revert of Remove redundant activation threshold for incremental marking.

src/heap/incremental-marking.cc

Index: src/heap/incremental-marking.cc
diff --git a/src/heap/incremental-marking.cc b/src/heap/incremental-marking.cc
index 7767bed6c3898a0eb093d8153c94999583eb729c..94d8d946f1ba27836d56a8c11e6a4042e35bf0aa 100644
--- a/src/heap/incremental-marking.cc
+++ b/src/heap/incremental-marking.cc
@@ -474,13 +474,21 @@
 
 
 bool IncrementalMarking::CanBeActivated() {
+#ifndef DEBUG
+  static const intptr_t kActivationThreshold = 8 * MB;
+#else
+  // TODO(gc) consider setting this to some low level so that some
+  // debug tests run with incremental marking and some without.
+  static const intptr_t kActivationThreshold = 0;
+#endif
   // Only start incremental marking in a safe state: 1) when incremental
   // marking is turned on, 2) when we are currently not in a GC, and
   // 3) when we are currently not serializing or deserializing the heap.
   // Don't switch on for very small heaps.
   return FLAG_incremental_marking && heap_->gc_state() == Heap::NOT_IN_GC &&
          heap_->deserialization_complete() &&
-         !heap_->isolate()->serializer_enabled();
+         !heap_->isolate()->serializer_enabled() &&
+         heap_->PromotedSpaceSizeOfObjects() > kActivationThreshold;
 }