[heap] Clear from-space live bytes in concurrent marker after scavenge.

Bug: chromium:757843
Change-Id: Ia3cf4e2126cbe567ae6f32fe4ccef631e028eaf9
Reviewed-on: https://chromium-review.googlesource.com/625879
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47515}

src/heap/heap.cc

@@ -1982,6 +1982,15 @@ void Heap::Scavenge() {
 
   incremental_marking()->UpdateMarkingWorklistAfterScavenge();
 
+  if (FLAG_concurrent_marking) {
+    // Ensure that concurrent marker does not track pages that are
+    // going to be unmapped.
+    for (Page* p : PageRange(new_space()->FromSpaceStart(),
+                             new_space()->FromSpaceEnd())) {
+      concurrent_marking()->ClearLiveness(p);
+    }
+  }
+
   ScavengeWeakObjectRetainer weak_object_retainer(this);
   ProcessYoungWeakReferences(&weak_object_retainer);
 

src/heap/mark-compact.cc

@@ -2529,6 +2529,11 @@ void MinorMarkCompactCollector::CollectGarbage() {
                              heap()->new_space()->FromSpaceEnd())) {
       DCHECK(!p->IsFlagSet(Page::SWEEP_TO_ITERATE));
       non_atomic_marking_state()->ClearLiveness(p);
+      if (FLAG_concurrent_marking) {
+        // Ensure that concurrent marker does not track pages that are
+        // going to be unmapped.
+        heap()->concurrent_marking()->ClearLiveness(p);
+      }
     }
   }