harmony-scoping: better error messages for let declarations in sloppy mode.

src/ast-value-factory.h

Index: src/ast-value-factory.h
diff --git a/src/ast-value-factory.h b/src/ast-value-factory.h
index 9ccd51147c2f3d16708f253a524a2047a2da401c..7b82e4a13e4080a73dc01036181153f9e5599f55 100644
--- a/src/ast-value-factory.h
+++ b/src/ast-value-factory.h
@@ -251,6 +251,7 @@ class AstValue : public ZoneObject {
   F(get_template_callsite, "GetTemplateCallSite")       \
   F(initialize_const_global, "initializeConstGlobal")   \
   F(initialize_var_global, "initializeVarGlobal")       \
+  F(let, "let")                                         \
   F(make_reference_error, "MakeReferenceErrorEmbedded") \
   F(make_syntax_error, "MakeSyntaxErrorEmbedded")       \
   F(make_type_error, "MakeTypeErrorEmbedded")           \