[heap] Do not perform black allocation in memory reducing mode.

Black allocation discards all old-space free-lists, which may be quite full when we perform memory reducing GCs.

BUG=chromium:599174
LOG=n

Review URL: https://codereview.chromium.org/1869493002

Cr-Commit-Position: refs/heads/master@{#35374}

src/heap/incremental-marking.cc

@@ -557,7 +557,7 @@ void IncrementalMarking::StartMarking() {
   IncrementalMarkingRootMarkingVisitor visitor(this);
   heap_->IterateStrongRoots(&visitor, VISIT_ONLY_STRONG);
 
-  if (FLAG_black_allocation) {
+  if (FLAG_black_allocation && !heap()->ShouldReduceMemory()) {
     StartBlackAllocation();
   }
 
@@ -580,10 +580,12 @@ void IncrementalMarking::StartBlackAllocation() {
 }
 
 void IncrementalMarking::FinishBlackAllocation() {
+  if (black_allocation_) {
     black_allocation_ = false;
     if (FLAG_trace_incremental_marking) {
       PrintF("[IncrementalMarking] Black allocation finished\n");
     }
+  }
 }
 
 void IncrementalMarking::MarkRoots() {
@@ -756,6 +758,12 @@ 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();
+    }
   }
 }