Support top-level field declaration and assignment in analyzer2dart.

pkg/compiler/lib/src/cps_ir/cps_ir_tracer.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.
 
 library dart2js.ir_tracer;
 
 import 'dart:async' show EventSink;
 
 import 'cps_ir_nodes.dart' as cps_ir hide Function;
 import '../tracer.dart';
@@ skipping 26 matching lines @@
     builder.visit(node);
 
     printNode(builder.entry);
     for (Block block in builder.cont2block.values) {
       printNode(block);
     }
     names = null;
   }
 
   visitFieldDefinition(cps_ir.FieldDefinition node) {
-    visitExecutableDefinition(node);
+    if (node.hasInitializer) {
+      visitExecutableDefinition(node);
+    }
   }
 
   visitFunctionDefinition(cps_ir.FunctionDefinition node) {
     visitExecutableDefinition(node);
   }
 
   int countUses(cps_ir.Definition definition) {
     int count = 0;
     cps_ir.Reference ref = definition.firstRef;
     while (ref != null) {
@@ skipping 278 matching lines @@
     }
     return block;
   }
 
   visitExecutableDefinition(cps_ir.ExecutableDefinition node) {
     entry = current_block = new Block(names.name(node), [], node.body);
     visit(node.body);
   }
 
   visitFieldDefinition(cps_ir.FieldDefinition node) {
-    visitExecutableDefinition(node);
+    if (node.hasInitializer) {
+      visitExecutableDefinition(node);
+    }
   }
 
   visitFunctionDefinition(cps_ir.FunctionDefinition node) {
     visitExecutableDefinition(node);
   }
 
   visitLetPrim(cps_ir.LetPrim exp) {
     visit(exp.body);
   }
 
@@ skipping 48 matching lines @@
     }
   }
 
   visitContinuation(cps_ir.Continuation c) {
     var old_node = current_block;
     current_block = getBlock(c);
     visit(c.body);
     current_block = old_node;
   }
 }