Fix async machinery (issue 22445 and possibly others to be triaged later).

runtime/vm/ast.h

Index: runtime/vm/ast.h
===================================================================
--- runtime/vm/ast.h	(revision 44105)
+++ runtime/vm/ast.h	(working copy)
@@ -159,8 +159,18 @@
 
 class AwaitNode : public AstNode {
  public:
-  AwaitNode(intptr_t token_pos, AstNode* expr)
-    : AstNode(token_pos), expr_(expr) { }
+  AwaitNode(intptr_t token_pos,
+            AstNode* expr,
+            LocalScope* try_scope,
+            int16_t try_index,
+            LocalScope* outer_try_scope,
+            intptr_t outer_try_index)
+    : AstNode(token_pos),
+      expr_(expr),
+      try_scope_(try_scope),
+      try_index_(try_index),
+      outer_try_scope_(outer_try_scope),
+      outer_try_index_(outer_try_index) { }
 
   void VisitChildren(AstNodeVisitor* visitor) const {
     expr_->Visit(visitor);
@@ -167,11 +177,19 @@
   }
 
   AstNode* expr() const { return expr_; }
+  LocalScope* try_scope() const { return try_scope_; }
+  int16_t try_index() const { return try_index_; }
+  LocalScope* outer_try_scope() const { return outer_try_scope_; }
+  int16_t outer_try_index() const { return outer_try_index_; }
 
   DECLARE_COMMON_NODE_FUNCTIONS(AwaitNode);
 
  private:
   AstNode* expr_;
+  LocalScope* try_scope_;
+  int16_t try_index_;
+  LocalScope* outer_try_scope_;
+  int16_t outer_try_index_;
 
   DISALLOW_COPY_AND_ASSIGN(AwaitNode);
 };