Support top-level field declaration and assignment in analyzer2dart.

pkg/compiler/lib/src/cps_ir/constant_propagation.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;
 
 /**
  * Propagates constants throughout the IR, and replaces branches with fixed
  * jumps as well as side-effect free expressions with known constant results.
  * Should be followed by the [ShrinkingReducer] pass.
@@ skipping 31 matching lines @@
         analyzer.reachableNodes, analyzer.node2value);
     transformer.transform(root);
   }
 
   void rewriteFunctionDefinition(FunctionDefinition root) {
     if (root.isAbstract) return;
     _rewriteExecutableDefinition(root);
   }
 
   void rewriteFieldDefinition(FieldDefinition root) {
+    if (!root.hasInitializer) return;
     _rewriteExecutableDefinition(root);
   }
 
 }
 
 /**
  * Uses the information from a preceding analysis pass in order to perform the
  * actual transformations on the CPS graph.
  */
 class _TransformingVisitor extends RecursiveVisitor {
@@ skipping 243 matching lines @@
     compiler.internalError(NO_LOCATION_SPANNABLE,
         "_ConstPropagationVisitor is stale, add missing visit overrides");
   }
 
   void visitFunctionDefinition(FunctionDefinition node) {
     node.parameters.forEach(visitParameter);
     setReachable(node.body);
   }
 
   void visitFieldDefinition(FieldDefinition node) {
-    setReachable(node.body);
+    if (node.hasInitializer) {
+      setReachable(node.body);
+    }
   }
 
   // Expressions.
 
   void visitLetPrim(LetPrim node) {
     visit(node.primitive); // No reason to delay visits to primitives.
     setReachable(node.body);
   }
 
   void visitLetCont(LetCont node) {
@@ skipping 364 matching lines @@
       return that;
     }
 
     if (this.constant == that.constant) {
       return this;
     }
 
     return NonConst;
   }
 }