Introduce await

runtime/vm/ast.h

Index: runtime/vm/ast.h
diff --git a/runtime/vm/ast.h b/runtime/vm/ast.h
index 26a6be23579056b760acada4ecfb14a297d92338..c88dc69d472cc492a9be1242fc55979985abdbb8 100644
--- a/runtime/vm/ast.h
+++ b/runtime/vm/ast.h
@@ -16,6 +16,7 @@
 namespace dart {
 
 #define FOR_EACH_NODE(V)                                                       \
+  V(Await)                                                                     \
   V(Return)                                                                    \
   V(Literal)                                                                   \
   V(Type)                                                                      \
@@ -146,6 +147,26 @@ class AstNode : public ZoneAllocated {
 };
 
 
+class AwaitNode : public AstNode {
+ public:
+  AwaitNode(intptr_t token_pos, AstNode* expr)
+    : AstNode(token_pos), expr_(expr) { }
+
+  void VisitChildren(AstNodeVisitor* visitor) const {
+    expr_->Visit(visitor);
+  }
+
+  AstNode* expr() const { return expr_; }
+
+  DECLARE_COMMON_NODE_FUNCTIONS(AwaitNode);
+
+ private:
+  AstNode* expr_;
+
+  DISALLOW_COPY_AND_ASSIGN(AwaitNode);
+};
+
+
 class SequenceNode : public AstNode {
  public:
   SequenceNode(intptr_t token_pos, LocalScope* scope)