Begin to compute constant expressions in resolution.

pkg/compiler/lib/src/deferred_load.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 deferred_load;
 
 import 'constants/expressions.dart';
 import 'constants/values.dart' show
     ConstantValue,
     ConstructedConstantValue,
@@ skipping 268 matching lines @@
 
       for (Element dependency in treeElements.allElements) {
         if (dependency.isLocal && !dependency.isFunction) continue;
         if (dependency.isErroneous) continue;
         if (dependency.isTypeVariable) continue;
 
         elements.add(dependency);
       }
       treeElements.forEachConstantNode((Node node, _) {
         // Explicitly depend on the backend constants.
-        constants.add(
-            backend.constants.getConstantValueForNode(node, treeElements));
+        ConstantValue value =
+            backend.constants.getConstantValueForNode(node, treeElements);
+        if (value != null) {
+          // TODO(johnniwinther): Assert that all constants have values when
+          // these are directly evaluated.
+          constants.add(value);
+        }
       });
       elements.addAll(treeElements.otherDependencies);
     }
 
     // TODO(sigurdm): How is metadata on a patch-class handled?
     for (MetadataAnnotation metadata in element.metadata) {
       ConstantValue constant =
           backend.constants.getConstantValueForMetadata(metadata);
       if (constant != null) {
         constants.add(constant);
@@ skipping 589 matching lines @@
         _importingLibrary = importingLibrary;
 
   String get importingLibraryName {
     String libraryName = _importingLibrary.getLibraryName();
     return libraryName == ""
       ? "<unnamed>"
       : libraryName;
   }
 
 }