[debugger] debug-evaluate should not not modify local values.

test/mjsunit/debug-evaluate-shadowed-context.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 --no-analyze-environment-liveness
 
 // 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.
@@ skipping 11 matching lines @@
         value = frame.evaluate("x").value();
       } catch (e) {
         value = e.name;
       }
       print(frame.sourceLineText());
       var expected = frame.sourceLineText().match(/\/\/ (.*$)/)[1];
       assertEquals(String(expected), String(value));
     }
     assertEquals("[object global]",
                  String(exec_state.frame(0).evaluate("this").value()));
-    exec_state.frame(0).evaluate("y = 'Y'");
+    assertEquals("y", exec_state.frame(0).evaluate("y").value());
+    assertEquals("a", exec_state.frame(0).evaluate("a").value());
     exec_state.frame(0).evaluate("a = 'A'");
     assertThrows(() => exec_state.frame(0).evaluate("z"), ReferenceError);
   } catch (e) {
     exception = e;
     print(e + e.stack);
   }
 }
 
 Debug.setListener(listener);
 
 var a = "a";
-assertEquals("Y", (function() {
+(function() {
   var x = 1;     // context allocate x
   (() => x);
   var y = "y";
   var z = "z";
   (function() {
     var x = 2;   // stack allocate shadowing x
     (function() {
       y;         // access y
       debugger;  // ReferenceError
     })();        // 2
   })();          // 1
   return y;
-})());
+})();
 
 assertEquals("A", a);
 a = "a";
 
-assertEquals("Y", (function() {
+(function() {
   var x = 1;     // context allocate x
   (() => x);
   var y = "y";
   var z = "z";
   (function() {
     var x = 2;   // stack allocate shadowing x
     (() => {
       y;
       a;
       this;      // context allocate receiver
       debugger;  // ReferenceError
     })();        // 2
   })();          // 1
   return y;
-})());
+})();
 
 assertEquals("A", a);
 
 Debug.setListener(null);
 assertNull(exception);