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

test/mjsunit/regress/regress-crbug-323936.js

 // Copyright 2014 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
+// Flags: --expose-debug-as debug --debug-eval-readonly-locals
 
 Debug = debug.Debug;
 
 var step = 0;
 var exception = null;
 
 function listener(event, exec_state, event_data, data) {
   if (event != Debug.DebugEvent.Break) return;
   try {
     if (step == 0) {
       assertEquals("error", exec_state.frame(0).evaluate("e").value());
-      exec_state.frame(0).evaluate("e = 'foo'");
-      exec_state.frame(0).evaluate("x = 'modified'");
+      exec_state.frame(0).evaluate("write_0('foo')");
+      exec_state.frame(0).evaluate("write_1('modified')");
     } else {
-      assertEquals("argument", exec_state.frame(0).evaluate("e").value());
-      exec_state.frame(0).evaluate("e = 'bar'");
+      assertEquals("foo", exec_state.frame(0).evaluate("e").value());
+      exec_state.frame(0).evaluate("write_2('bar')");
     }
     step++;
   } catch (e) {
     print(e + e.stack);
     exception = e;
   }
 }
 
 Debug.setListener(listener);
 
 function f(e, x) {
   try {
     throw "error";
   } catch(e) {
+    // 'e' and 'x' bind to the argument due to hoisting
+    function write_0(v) { e = v }
+    function write_1(v) { x = v }
     debugger;
-    assertEquals("foo", e);
+    assertEquals("error", e);
   }
+  function write_2(v) { e = v }
   debugger;
   assertEquals("bar", e);
   assertEquals("modified", x);
 }
 
 f("argument")
 assertNull(exception);
 assertEquals(2, step);