Make let variables fresh in each iteration of a for-loop.

test/mjsunit/harmony/debug-blockscopes.js

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 394 matching lines @@
 BeginTest("For loop 3");
 
 function for_loop_3() {
   for (let x = 3; x < 4; ++x) {
     debugger;
   }
 }
 
 listener_delegate = function(exec_state) {
   CheckScopeChain([debug.ScopeType.Block,
+                   debug.ScopeType.Block,
                    debug.ScopeType.Local,
                    debug.ScopeType.Global], exec_state);
   CheckScopeContent({x:3}, 0, exec_state);
-  CheckScopeContent({}, 1, exec_state);
+  CheckScopeContent({x:3}, 1, exec_state);
+  CheckScopeContent({}, 2, exec_state);
 };
 for_loop_3();
 EndTest();
 
 
 // For loop with a block scoped let variable shadowing the iteration variable.
 BeginTest("For loop 4");
 
 function for_loop_4() {
   for (let x = 3; x < 4; ++x) {
     let x = 5;
     debugger;
   }
 }
 
 listener_delegate = function(exec_state) {
   CheckScopeChain([debug.ScopeType.Block,
                    debug.ScopeType.Block,
+                   debug.ScopeType.Block,
                    debug.ScopeType.Local,
                    debug.ScopeType.Global], exec_state);
   CheckScopeContent({x:5}, 0, exec_state);
   CheckScopeContent({x:3}, 1, exec_state);
-  CheckScopeContent({}, 2, exec_state);
+  CheckScopeContent({x:3}, 2, exec_state);
+  CheckScopeContent({}, 3, exec_state);
 };
 for_loop_4();
 EndTest();
 
 
 // For loop with two variable declarations.
 BeginTest("For loop 5");
 
 function for_loop_5() {
   for (let x = 3, y = 5; x < 4; ++x) {
     debugger;
   }
 }
 
 listener_delegate = function(exec_state) {
   CheckScopeChain([debug.ScopeType.Block,
+                   debug.ScopeType.Block,
                    debug.ScopeType.Local,
                    debug.ScopeType.Global], exec_state);
   CheckScopeContent({x:3,y:5}, 0, exec_state);
-  CheckScopeContent({}, 1, exec_state);
+  CheckScopeContent({x:3,y:5}, 1, exec_state);
+  CheckScopeContent({}, 2, exec_state);
 };
 for_loop_5();
 EndTest();