Ensure we align zone memory at 8 byte boundaries on all platforms

test/unittests/zone/zone-unittest.cc

+// Copyright 2017 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/zone/zone.h"
+
+#include "src/zone/accounting-allocator.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace v8 {
+namespace internal {
+
+TEST(Zone, 8ByteAlignment) {
+  AccountingAllocator allocator;
+  Zone zone(&allocator, ZONE_NAME);
+
+  for (size_t i = 0; i < 16; ++i) {
+    ASSERT_EQ(reinterpret_cast<intptr_t>(zone.New(i)) % 8, 0);
+  }
+}
+
+}  // namespace internal
+}  // namespace v8