Extend AST with basic module constructs (yet unused).

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 8b5baffcb38b445f72cb05d5bd0fb38c03be950b..e2505876d842034f378d1dc229701eff36232fab 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -6582,6 +6582,31 @@ void HGraphBuilder::HandleVariableDeclaration(VariableProxy* proxy,
 }
 
 
+void HGraphBuilder::VisitModuleDeclaration(ModuleDeclaration* decl) {
+  // TODO(rossberg)
+}
+
+
+void HGraphBuilder::VisitModuleLiteral(ModuleLiteral* module) {
+  // TODO(rossberg)
+}
+
+
+void HGraphBuilder::VisitModuleVariable(ModuleVariable* module) {
+  // TODO(rossberg)
+}
+
+
+void HGraphBuilder::VisitModulePath(ModulePath* module) {
+  // TODO(rossberg)
+}
+
+
+void HGraphBuilder::VisitModuleUrl(ModuleUrl* module) {
+  // TODO(rossberg)
+}
+
+
 // Generators for inline runtime functions.
 // Support for types.
 void HGraphBuilder::GenerateIsSmi(CallRuntime* call) {