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

test/mjsunit/debug-evaluate-declaration.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
+
+// Test that debug-evaluate only resolves variables that are used by
+// the function inside which we debug-evaluate. This is to avoid
+// incorrect variable resolution when a context-allocated variable is
+// shadowed by a stack-allocated variable.
+
+"use strict";
+
+var 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("var x = 2");
+    exec_state.frame(0).evaluate("'use strict'; let y = 3");
+    exec_state.frame(0).evaluate("var z = 4");
+    exec_state.frame(0).evaluate("function bar() { return 5; }");
+  } catch (e) {
+    exception = e;
+    print(e + e.stack);
+  }
+}
+
+Debug.setListener(listener);
+
+var z = 1;
+
+(function() {
+  debugger;
+})();
+
+assertEquals(2, x);                     // declaration
+assertThrows(() => y, ReferenceError);  // let-declaration does not stick
+assertEquals(4, z);                     // re-declaration
+assertEquals(5, bar());                 // function declaration
+
+Debug.setListener(null);
+assertNull(exception);