[debugger] fix debug-evaluate wrt shadowed context var.

test/mjsunit/debug-evaluate-modify-catch-block-scope.js

+// Copyright 2015 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;
+function listener(event, exec_state, event_data, data) {
+  if (event != Debug.DebugEvent.Break) return;
+  try {
+    exec_state.frame(0).evaluate("bar()");
+  } catch (e) {
+    exception = e;
+    print(e + e.stack);
+  }
+}
+
+Debug.setListener(listener);
+
+(function() {
+  "use strict";
+  try {
+    throw 1;
+  } catch (e) {
+    let a = 1;
+    function bar() {
+      a = 2;  // this has no effect, when called from debug-eval
+      e = 2;  // this has no effect, when called from debug-eval.
+    }
+    debugger;
+    assertEquals(1, a);
+    assertEquals(1, e);
+  }
+})();
+
+Debug.setListener(null);