Reland of "[heap] Divide available memory upon compaction tasks"

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 75b7ec1fa698f824e2e82c57da0cb9947132b08f..8aa6fb85876ef8c7df392e87c0d04fedb5dc28c7 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -3047,6 +3047,7 @@ void Heap::CreateFillerObjectAt(Address addr, int size) {
     filler->set_map_no_write_barrier(
         reinterpret_cast<Map*>(root(kTwoPointerFillerMapRootIndex)));
   } else {
+    DCHECK_GT(size, 2 * kPointerSize);
     filler->set_map_no_write_barrier(
         reinterpret_cast<Map*>(root(kFreeSpaceMapRootIndex)));
     FreeSpace::cast(filler)->nobarrier_set_size(size);