[debugger] allow debug-evaluate to change stack and context values.

test/mjsunit/debug-evaluate-modify-this.js

Index: test/mjsunit/debug-evaluate-modify-this.js
diff --git a/test/mjsunit/debug-evaluate-modify-this.js b/test/mjsunit/debug-evaluate-modify-this.js
new file mode 100644
index 0000000000000000000000000000000000000000..930f6ed0431078cd02d6253bdedb1dd4f76560b1
--- /dev/null
+++ b/test/mjsunit/debug-evaluate-modify-this.js
@@ -0,0 +1,33 @@
+// 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
+
+Debug = debug.Debug
+
+var exception = null;
+
+var f = () => { debugger; }
+var g = function() { debugger; }
+var h = (function() { return () => { debugger; }; }).call({});
+
+function listener(event, exec_state, event_data, data) {
+  if (event != Debug.DebugEvent.Break) return;
+  try {
+    assertThrows(() => exec_state.frame(0).evaluate("this = 2"));
+  } catch (e) {
+    exception = e;
+    print("Caught something. " + e + " " + e.stack);
+  };
+};
+
+Debug.setListener(listener);
+
+f();
+g();
+g.call({});
+h();
+
+Debug.setListener(null);
+assertNull(exception);