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

test/mjsunit/regress-3225.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 debug_step = 0;
 var failure = null;
 
 function listener(event, exec_state, event_data, data) {
   if (event != Debug.DebugEvent.Break) return;
   try {
     if (debug_step == 0) {
       assertEquals(1, exec_state.frame(0).evaluate('a').value());
       assertEquals(3, exec_state.frame(0).evaluate('b').value());
-      exec_state.frame(0).evaluate("a = 4").value();
+      exec_state.frame(0).evaluate("a = 4").value();  // no effect.
       debug_step++;
     } else {
-      assertEquals(4, exec_state.frame(0).evaluate('a').value());
+      assertEquals(1, exec_state.frame(0).evaluate('a').value());
       assertEquals(3, exec_state.frame(0).evaluate('b').value());
-      exec_state.frame(0).evaluate("b = 5").value();
+      exec_state.frame(0).evaluate("set_a_to_5()");
+      exec_state.frame(0).evaluate("b = 5").value();  // no effect.
     }
   } catch (e) {
     failure = e;
   }
 }
 
 Debug.setListener(listener);
 
 function* generator(a, b) {
+  function set_a_to_5() { a = 5 }
   var b = 3;  // Shadows a parameter.
   debugger;
   yield a;
   yield b;
   debugger;
+  yield a;
   return b;
 }
 
 var foo = generator(1, 2);
 
-assertEquals(4, foo.next().value);
+assertEquals(1, foo.next().value);
 assertEquals(3, foo.next().value);
 assertEquals(5, foo.next().value);
+assertEquals(3, foo.next().value);
 assertNull(failure);
 
 Debug.setListener(null);