[es7] implement |do| expressions proposal

src/ast-expression-visitor.cc

Index: src/ast-expression-visitor.cc
diff --git a/src/ast-expression-visitor.cc b/src/ast-expression-visitor.cc
index 4a4bc6068597fa728ea17fa6a4d3e9dc80a662ec..63d1f06cf71a567cbdf219a9a9b52bd5c3412de1 100644
--- a/src/ast-expression-visitor.cc
+++ b/src/ast-expression-visitor.cc
@@ -196,6 +196,12 @@ void AstExpressionVisitor::VisitNativeFunctionLiteral(
     NativeFunctionLiteral* expr) {}
 
 
+void AstExpressionVisitor::VisitDoExpression(DoExpression* expr) {
+  RECURSE(VisitBlock(expr->block()));
+  RECURSE(VisitVariableProxy(expr->result()));
+}
+
+
 void AstExpressionVisitor::VisitConditional(Conditional* expr) {
   RECURSE(Visit(expr->condition()));
   RECURSE(Visit(expr->then_expression()));