[es7] implement |do| expressions proposal

src/typing.cc

Index: src/typing.cc
diff --git a/src/typing.cc b/src/typing.cc
index fcf5f5a00808bc33876f6a8c23e181fe7cc6dfaf..78f3f04b336498ae5c5f3ebbf531ed0ae4ac7f70 100644
--- a/src/typing.cc
+++ b/src/typing.cc
@@ -349,6 +349,13 @@ void AstTyper::VisitNativeFunctionLiteral(NativeFunctionLiteral* expr) {
 }
 
 
+void AstTyper::VisitDoExpression(DoExpression* expr) {
+  RECURSE(VisitBlock(expr->block()));
+  RECURSE(VisitVariableProxy(expr->result()));
+  NarrowType(expr, expr->result()->bounds());
+}
+
+
 void AstTyper::VisitConditional(Conditional* expr) {
   // Collect type feedback.
   expr->condition()->RecordToBooleanTypeFeedback(oracle());