Reland of [parsing] Fix maybe-assigned for loop variables.

src/parsing/pattern-rewriter.cc

 // 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.
 
 #include "src/ast/ast.h"
 #include "src/messages.h"
 #include "src/objects-inl.h"
 #include "src/parsing/parameter-initializer-rewriter.h"
 #include "src/parsing/parser.h"
 
@@ skipping 159 matching lines @@
   if (names_) {
     names_->Add(name, zone());
   }
 
   Scope* var_init_scope = descriptor_->scope;
   MarkTopLevelVariableAsAssigned(var_init_scope, proxy);
 
   // If there's no initializer, we're done.
   if (value == nullptr) return;
 
+  MarkLoopVariableAsAssigned(var_init_scope, proxy->var());
+
   // A declaration of the form:
   //
   //    var v = x;
   //
   // is syntactic sugar for:
   //
   //    var v; v = x;
   //
   // In particular, we need to re-lookup 'v' as it may be a different
   // 'v' than the 'v' in the declaration (e.g., if we are inside a
@@ skipping 568 matching lines @@
 NOT_A_PATTERN(TryFinallyStatement)
 NOT_A_PATTERN(UnaryOperation)
 NOT_A_PATTERN(VariableDeclaration)
 NOT_A_PATTERN(WhileStatement)
 NOT_A_PATTERN(WithStatement)
 NOT_A_PATTERN(Yield)
 
 #undef NOT_A_PATTERN
 }  // namespace internal
 }  // namespace v8