[heap] Start unmapper tasks for freed young large pages

This fixes the case of accumulating large pages after scavenges if
there is no mark-compact GC.

Bug: chromium:934453
Change-Id: Ide57c64ae985cc79ad9f477a759ab729f894c73b
Reviewed-on: https://chromium-review.googlesource.com/c/1482740Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59838}

src/heap/spaces.cc

@@ -3797,12 +3797,14 @@ void NewLargeObjectSpace::FreeDeadObjects(
     const std::function<bool(HeapObject)>& is_dead) {
   bool is_marking = heap()->incremental_marking()->IsMarking();
   size_t surviving_object_size = 0;
+  bool freed_pages = false;
   for (auto it = begin(); it != end();) {
     LargePage* page = *it;
     it++;
     HeapObject object = page->GetObject();
     size_t size = static_cast<size_t>(object->Size());
     if (is_dead(object)) {
+      freed_pages = true;
       RemovePage(page, size);
       heap()->memory_allocator()->Free<MemoryAllocator::kPreFreeAndQueue>(page);
       if (FLAG_concurrent_marking && is_marking) {
@@ -3815,6 +3817,9 @@ void NewLargeObjectSpace::FreeDeadObjects(
   // Right-trimming does not update the objects_size_ counter. We are lazily
   // updating it after every GC.
   objects_size_ = surviving_object_size;
+  if (freed_pages) {
+    heap()->memory_allocator()->unmapper()->FreeQueuedChunks();
+  }
 }
 
 void NewLargeObjectSpace::SetCapacity(size_t capacity) {