[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 d534d1f0f036c1210175cd7f7b89505c7016b860..bbe8e9b67639fdf46672b61eb5edc73276f55704 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()));