Reland of "[heap] Parallel newspace evacuation, semispace copy, and compaction \o/"

test/cctest/heap/test-heap.cc

Index: test/cctest/heap/test-heap.cc
diff --git a/test/cctest/heap/test-heap.cc b/test/cctest/heap/test-heap.cc
index 6df355d289d30ad8168c3030b5812cb234126808..274cf9b58e3839c5ddd9c47f87fb4fadc52aa328 100644
--- a/test/cctest/heap/test-heap.cc
+++ b/test/cctest/heap/test-heap.cc
@@ -3514,6 +3514,13 @@ TEST(ReleaseOverReservedPages) {
   // The optimizer can allocate stuff, messing up the test.
   i::FLAG_crankshaft = false;
   i::FLAG_always_opt = false;
+  // Parallel compaction increases fragmentation, depending on how existing
+  // memory is distributed. Since this is non-deterministic because of
+  // concurrent sweeping, we disable it for this test.
+  i::FLAG_parallel_compaction = false;
+  // Concurrent sweeping adds non determinism, depending on when memory is
+  // available for further reuse.
+  i::FLAG_concurrent_sweeping = false;
   CcTest::InitializeVM();
   Isolate* isolate = CcTest::i_isolate();
   Factory* factory = isolate->factory();