Implement proper scoping for "this" in arrow functions

src/scopeinfo.cc

 // Copyright 2011 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 <stdlib.h>
 
 #include "src/v8.h"
 
 #include "src/scopeinfo.h"
 #include "src/scopes.h"
@@ skipping 261 matching lines @@
 }
 
 
 bool ScopeInfo::LocalIsSynthetic(int var) {
   DCHECK(0 <= var && var < LocalCount());
   // There's currently no flag stored on the ScopeInfo to indicate that a
   // variable is a compiler-introduced temporary. However, to avoid conflict
   // with user declarations, the current temporaries like .generator_object and
   // .result start with a dot, so we can use that as a flag. It's a hack!
   Handle<String> name(LocalName(var));
-  return name->length() > 0 && name->Get(0) == '.';
+  return (name->length() > 0 && name->Get(0) == '.') ||
+         (name->length() == 4 && name->Get(0) == 't' && name->Get(1) == 'h' &&
+          name->Get(2) == 'i' && name->Get(3) == 's');
 }
 
 
 int ScopeInfo::StackSlotIndex(String* name) {
   DCHECK(name->IsInternalizedString());
   if (length() > 0) {
     int start = StackLocalEntriesIndex();
     int end = StackLocalEntriesIndex() + StackLocalCount();
     for (int i = start; i < end; ++i) {
       if (name == get(i)) {
@@ skipping 271 matching lines @@
     info->set_name(i, *(it.export_name()->string()));
     info->set_mode(i, var->mode());
     DCHECK(var->index() >= 0);
     info->set_index(i, var->index());
   }
   DCHECK(i == info->length());
   return info;
 }
 
 } }  // namespace v8::internal