[heap] Turn on black allocation during marking finalization to avoid floating garbage.

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 85e9f6d7763820d1c3617428228f234f053de4e4..167c13a4fee7bb3d268189d64ac762663b9c7848 100644
--- a/src/heap/incremental-marking.cc
+++ b/src/heap/incremental-marking.cc
@@ -557,10 +557,6 @@ void IncrementalMarking::StartMarking() {
   IncrementalMarkingRootMarkingVisitor visitor(this);
   heap_->IterateStrongRoots(&visitor, VISIT_ONLY_STRONG);
 
-  if (FLAG_black_allocation && !heap()->ShouldReduceMemory()) {
-    StartBlackAllocation();
-  }
-
   // Ready to start incremental marking.
   if (FLAG_trace_incremental_marking) {
     PrintF("[IncrementalMarking] Running\n");
@@ -761,12 +757,13 @@ void IncrementalMarking::FinalizeIncrementally() {
       (marking_progress <
        FLAG_min_progress_during_incremental_marking_finalization)) {
     finalize_marking_completed_ = true;
+  }
 
-    // If black allocation was not enabled earlier, start black allocation
-    // here.
-    if (FLAG_black_allocation && !black_allocation_) {
-      StartBlackAllocation();
-    }
+  if (FLAG_black_allocation && !heap()->ShouldReduceMemory() &&
+      !black_allocation_) {
+    // TODO(hpayer): Move to an earlier point as soon as we make faster marking
+    // progress.
+    StartBlackAllocation();
   }
 }