[debugger] add test for debug evaluate.

This test would have failed prior to 58524d6d.

R=verwaest@chromium.org

Review-Url: https://codereview.chromium.org/2235323003
Cr-Commit-Position: refs/heads/master@{#38610}

test/mjsunit/debug-evaluate-shadowed-context-2.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.
+
+// Flags: --expose-debug-as debug --no-analyze-environment-liveness
+
+// Test that debug-evaluate correctly collects free outer variables
+// and does not get confused by variables in nested scopes.
+
+Debug = debug.Debug
+
+var exception = null;
+function listener(event, exec_state, event_data, data) {
+  if (event != Debug.DebugEvent.Break) return;
+  try {
+    assertThrows(() => exec_state.frame(0).evaluate("x").value());
+  } catch (e) {
+    exception = e;
+    print(e + e.stack);
+  }
+}
+
+Debug.setListener(listener);
+
+(function() {
+  var x = 1;     // context allocate x
+  (() => x);
+  (function() {
+    var x = 2;   // stack allocate shadowing x
+    (function() {
+      {          // context allocate x in a nested scope
+        let x = 3;
+        (() => x);
+      }
+      debugger;
+    })();
+  })();
+})();
+
+Debug.setListener(null);
+assertNull(exception);