[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
 
-function f() {
-  1;
-  2;
-  3;
-}
+Debug = debug.Debug
 
-var Debug = debug.Debug;
 var exception = null;
-var breaks = [];
-
 function listener(event, exec_state, event_data, data) {
   if (event != Debug.DebugEvent.Break) return;
   try {
-    Debug.debuggerFlags().breakPointsActive.setValue(false);
-    breaks.push(exec_state.frame().sourceLineText().trimLeft());
-    exec_state.prepareStep(Debug.StepAction.StepIn, 1);
+    exec_state.frame(0).evaluate("bar()");
   } catch (e) {
     exception = e;
+    print(e + e.stack);
   }
 }
 
 Debug.setListener(listener);
-Debug.setBreakPoint(f, 0, 0);
 
-f();
+(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);
-Debug.debuggerFlags().breakPointsActive.setValue(true);
-
 assertNull(exception);
-assertEquals(breaks, ["1;", "2;", "3;", "}", "Debug.setListener(null);"]);