Patches to support Dart VM patch files in dart2js.

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

Index: pkg/compiler/lib/src/tree/nodes.dart
diff --git a/pkg/compiler/lib/src/tree/nodes.dart b/pkg/compiler/lib/src/tree/nodes.dart
index 9335fef859d950573231a6ffac2c9611bc51107a..1a607bac1d26b052e263a4aa240d9be555da8759 100644
--- a/pkg/compiler/lib/src/tree/nodes.dart
+++ b/pkg/compiler/lib/src/tree/nodes.dart
@@ -2976,16 +2976,17 @@ class CatchBlock extends Node {
 
   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) {