Avoid dynamic lookup when initializing let declared variables.

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 397 matching lines @@
                    debug.ScopeType.With,
                    debug.ScopeType.Local,
                    debug.ScopeType.Global], exec_state);
   CheckScopeContent({a:2,b:1}, 0, exec_state);
   CheckScopeContent({a:1,b:2}, 1, exec_state);
 };
 with_block_4();
 EndTest();
 
 
+// With block and a block local variable.
+BeginTest("With block 5");
+
+function with_block_5() {
+  with({a:1}) {
+    let a = 2;
+    debugger;
+  }
+}
+
+listener_delegate = function(exec_state) {
+  CheckScopeChain([debug.ScopeType.Block,
+                   debug.ScopeType.With,
+                   debug.ScopeType.Local,
+                   debug.ScopeType.Global], exec_state);
+  CheckScopeContent({a:2}, 0, exec_state);
+  CheckScopeContent({a:1}, 1, exec_state);
+};
+with_block_5();
+EndTest();
+
+
 // Simple closure formed by returning an inner function referering to an outer
 // block local variable and an outer function's parameter.
 BeginTest("Closure 1");
 
 function closure_1(a) {
   var x = 2;
   let y = 3;
   if (true) {
     let z = 4;
     function f() {
       debugger;
       return a + x + y + z;
     };
     return f;
   }
 }
 
 listener_delegate = function(exec_state) {
   CheckScopeChain([debug.ScopeType.Local,
                    debug.ScopeType.Block,
                    debug.ScopeType.Closure,
                    debug.ScopeType.Global], exec_state);
   CheckScopeContent({}, 0, exec_state);
   CheckScopeContent({a:1,x:2,y:3}, 2, exec_state);
 };
 closure_1(1)();
 EndTest();