Support top-level field declaration and assignment in analyzer2dart.

pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart

 // Copyright (c) 2014, 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.
 
 part of dart2js.optimizers;
 
 /**
  * [[ShrinkingReducer]] applies shrinking reductions to CPS terms as described
  * in 'Compiling with Continuations, Continued' by Andrew Kennedy.
  */
@@ skipping 16 matching lines @@
     // Process the worklist.
     while (_worklist.isNotEmpty) {
       _ReductionTask task = _worklist.first;
       _worklist.remove(task);
       _processTask(task);
     }
   }
 
   /// Applies shrinking reductions to root, mutating root in the process.
   void rewriteFieldDefinition(FieldDefinition root) {
+    if (!root.hasInitializer) return;
     rewriteExecutableDefinition(root);
   }
 
   /// Applies shrinking reductions to root, mutating root in the process.
   void rewriteFunctionDefinition(FunctionDefinition root) {
     if (root.isAbstract) return;
     rewriteExecutableDefinition(root);
   }
 
   /// Removes the given node from the CPS graph, replacing it with its body
@@ skipping 402 matching lines @@
   }
 
   String toString() => "$kind: $node";
 }
 
 /// A dummy class used solely to mark nodes as deleted once they are removed
 /// from a term.
 class _DeletedNode extends Node {
   accept(_) => null;
 }