Skip spurious constants in deferred computation.

pkg/compiler/lib/src/dart_backend/backend.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.
 
 part of dart_backend;
 
 // TODO(ahe): This class is simply wrong.  This backend should use
 // elements when it can, not AST nodes.  Perhaps a [Map<Element,
 // TreeElements>] is what is needed.
 class ElementAst {
@@ skipping 447 matching lines @@
   DartConstantTask(Compiler compiler)
       : this.constantCompiler = new DartConstantCompiler(compiler),
         super(compiler);
 
   String get name => 'ConstantHandler';
 
   @override
   ConstantSystem get constantSystem => constantCompiler.constantSystem;
 
   @override
+  bool hasConstantValue(ConstantExpression expression) {
+    return constantCompiler.hasConstantValue(expression);
+  }
+
+  @override
   ConstantValue getConstantValue(ConstantExpression expression) {
     return constantCompiler.getConstantValue(expression);
   }
 
   @override
   ConstantValue getConstantValueForVariable(VariableElement element) {
     return constantCompiler.getConstantValueForVariable(element);
   }
 
   @override
@@ skipping 51 matching lines @@
   }
 
   // TODO(johnniwinther): Remove this when values are computed from the
   // expressions.
   @override
   void copyConstantValues(DartConstantTask task) {
     constantCompiler.constantValueMap
         .addAll(task.constantCompiler.constantValueMap);
   }
 }