[heap] Simplify adjusting of live bytes.

test/cctest/heap/test-spaces.cc

Index: test/cctest/heap/test-spaces.cc
diff --git a/test/cctest/heap/test-spaces.cc b/test/cctest/heap/test-spaces.cc
index 9a7585d68180dd2269cce67000747f1d723574eb..763b7038ad09724848c2355a5d2186617e9965ea 100644
--- a/test/cctest/heap/test-spaces.cc
+++ b/test/cctest/heap/test-spaces.cc
@@ -797,5 +797,38 @@ TEST(ShrinkPageToHighWaterMarkTwoWordFiller) {
   CHECK_EQ(0u, shrinked);
 }
 
+HEAP_TEST(AdjustBytes) {
+  CcTest::InitializeVM();
+  Isolate* isolate = CcTest::i_isolate();
+  HandleScope scope(isolate);
+  Heap* heap = isolate->heap();
+  for (int i = 0; i < 3; i++) {
+    heap->CollectGarbage(OLD_SPACE, i::GarbageCollectionReason::kTesting);
+  }
+  heap->mark_compact_collector()->EnsureSweepingCompleted();
+  heap::SealCurrentObjects(CcTest::heap());
+
+  Handle<FixedArray> array = isolate->factory()->NewFixedArray(5000, TENURED);
+
+  heap->CollectGarbage(OLD_SPACE, i::GarbageCollectionReason::kTesting);
+  heap->delay_sweeper_tasks_for_testing_ = false;
+
+  size_t size_before = heap->SizeOfObjects();
+  heap->RightTrimFixedArray(*array, 1000);
+  heap->mark_compact_collector()->sweeper().StartSweeperTasks();
+  heap->mark_compact_collector()->EnsureSweepingCompleted();
+  size_t size_after = heap->SizeOfObjects();
+  // Right trimming during sweeping does not affect size counters.
+  CHECK_EQ(size_before, size_after);
+  heap->RightTrimFixedArray(*array, 1000);
+  size_after = heap->SizeOfObjects();
+  // Right trimming before incremental marking runs does not affect size
+  // counters.
+  CHECK_EQ(size_before, size_after);
+  heap->CollectGarbage(OLD_SPACE, i::GarbageCollectionReason::kTesting);
+  size_after = heap->SizeOfObjects();
+  CHECK_EQ(size_before, size_after + 2000 * kPointerSize);
+}
+
 }  // namespace internal
 }  // namespace v8