[debugger] Various break-related functionality in test wrapper

test/debugger/wrapper/break-on-debugger-stmt.js

+// Copyright 2016 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.
+
+function f() { debugger; debugger; }
+
+const Debug = new DebugWrapper();
+Debug.enable();
+
+let breakEventCount = 0;
+Debug.setListener(function(event, exec_state, event_data, data) {
+  if (event != DebugEvent.Break) return;
+  breakEventCount++;
+});
+
+assertEquals(0, breakEventCount);
+f();
+f();
+f();
+assertEquals(6, breakEventCount);