Patches to support Dart VM patch files in dart2js.

pkg/compiler/lib/src/tree/nodes.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:collection' show IterableMixin;
 
 import '../common.dart';
 import '../tokens/precedence_constants.dart' as Precedence show FUNCTION_INFO;
 import '../tokens/token.dart' show BeginGroupToken, Token;
 import '../tokens/token_constants.dart' as Tokens
@@ skipping 2958 matching lines @@
       this.type, this.formals, this.block, this.onKeyword, this.catchKeyword);
 
   CatchBlock asCatchBlock() => this;
 
   accept(Visitor visitor) => visitor.visitCatchBlock(this);
 
   accept1(Visitor1 visitor, arg) => visitor.visitCatchBlock(this, arg);
 
   Node get exception {
     if (formals == null || formals.nodes.isEmpty) return null;
-    VariableDefinitions declarations = formals.nodes.head;
-    return declarations.definitions.nodes.head;
+    VariableDefinitions declarations =
+        formals.nodes.head.asVariableDefinitions();
+    return declarations?.definitions?.nodes?.head;
   }
 
   Node get trace {
     if (formals == null || formals.nodes.isEmpty) return null;
     Link<Node> declarations = formals.nodes.tail;
     if (declarations.isEmpty) return null;
-    VariableDefinitions head = declarations.head;
-    return head.definitions.nodes.head;
+    VariableDefinitions head = declarations.head.asVariableDefinitions();
+    return head?.definitions?.nodes?.head;
   }
 
   visitChildren(Visitor visitor) {
     if (type != null) type.accept(visitor);
     if (formals != null) formals.accept(visitor);
     block.accept(visitor);
   }
 
   visitChildren1(Visitor1 visitor, arg) {
     if (type != null) type.accept1(visitor, arg);
@@ skipping 115 matching lines @@
 
   // VariableDefinitions.
   get metadata => null;
   get type => null;
 
   // Typedef.
   get typeParameters => null;
   get formals => null;
   get typedefKeyword => null;
 }