Split function block scoping into a separate flag

src/parser.cc

Index: src/parser.cc
diff --git a/src/parser.cc b/src/parser.cc
index 45202cb3a82b922c7d487061cfff03578cc3a3c9..6d143965bef7b6cba4c3afa4ff5dc487f455a3ed 100644
--- a/src/parser.cc
+++ b/src/parser.cc
@@ -911,6 +911,7 @@ Parser::Parser(ParseInfo* info)
   set_allow_lazy(info->allow_lazy_parsing());
   set_allow_natives(FLAG_allow_natives_syntax || info->is_native());
   set_allow_harmony_arrow_functions(FLAG_harmony_arrow_functions);
+  set_allow_harmony_block_function(FLAG_harmony_block_function);
   set_allow_harmony_sloppy(FLAG_harmony_sloppy);
   set_allow_harmony_sloppy_let(FLAG_harmony_sloppy_let);
   set_allow_harmony_rest_parameters(FLAG_harmony_rest_parameters);
@@ -2222,8 +2223,10 @@ Statement* Parser::ParseFunctionDeclaration(
   VariableMode mode =
       is_strong(language_mode())
           ? CONST
-          : (is_strict(language_mode()) || allow_harmony_sloppy()) &&
-              !scope_->is_declaration_scope() ? LET : VAR;
+          : (is_strict(language_mode()) || allow_harmony_block_function()) &&
+                    !scope_->is_declaration_scope()
+                ? LET
+                : VAR;
   VariableProxy* proxy = NewUnresolved(name, mode);
   Declaration* declaration =
       factory()->NewFunctionDeclaration(proxy, mode, fun, scope_, pos);