Introduce per-isolate assert scopes and API to guard JS execution.

src/assert-scope.cc

+// Copyright 2014 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 "assert-scope.h"
+#include "v8.h"
+
+namespace v8 {
+namespace internal {
+
+uint32_t PerIsolateAssertBase::GetData(Isolate* isolate) {
+  return isolate->per_isolate_assert_data();
+}
+
+
+void PerIsolateAssertBase::SetData(Isolate* isolate, uint32_t data) {
+  isolate->set_per_isolate_assert_data(data);
+}
+
+} }  // namespace v8::internal