Implement ES2015 labelled function declaration restrictions

src/parsing/parser-base.h

Index: src/parsing/parser-base.h
diff --git a/src/parsing/parser-base.h b/src/parsing/parser-base.h
index 5415eef42c78180c1e73e65d225882b1918ce8af..59108681c545a6a7f2ada01174895b19c3d042ef 100644
--- a/src/parsing/parser-base.h
+++ b/src/parsing/parser-base.h
@@ -24,6 +24,10 @@ enum FunctionNameValidity {
   kFunctionNameValidityUnknown
 };
 
+enum AllowLabelledFunctionStatement {
+  kAllowLabelledFunctionStatement,
+  kDisallowLabelledFunctionStatement,
+};
 
 struct FormalParametersBase {
   explicit FormalParametersBase(Scope* scope) : scope(scope) {}