Use ConstExp for storing constants.

sdk/lib/_internal/compiler/implementation/js_emitter/container_builder.dart

 // Copyright (c) 2013, 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.js_emitter;
 
 /// This class should morph into something that makes it easy to build
 /// JavaScript representations of libraries, class-sides, and instance-sides.
 /// Initially, it is just a placeholder for code that is moved from
 /// [CodeEmitterTask].
@@ skipping 78 matching lines @@
       } else {
         int index = names.indexOf(element.name);
         if (index != -1) {
           indexOfLastOptionalArgumentInParameters = count;
           // The order of the named arguments is not the same as the
           // one in the real method (which is in Dart source order).
           argumentsBuffer[count] = js('#', jsName);
           parametersBuffer[optionalParameterStart + index] =
               new jsAst.Parameter(jsName);
         } else {
-          Constant value = handler.getConstantForVariable(element);
-          if (value == null) {
+          ConstExp constant = handler.getConstantForVariable(element);
+          if (constant == null) {
             argumentsBuffer[count] = task.constantReference(new NullConstant());
           } else {
+            Constant value = constant.value;
             if (!value.isNull) {
               // If the value is the null constant, we should not pass it
               // down to the native method.
               indexOfLastOptionalArgumentInParameters = count;
             }
             argumentsBuffer[count] = task.constantReference(value);
           }
         }
       }
       count++;
@@ skipping 396 matching lines @@
             task.metadataEmitter.reifyDefaultArguments(member).map(js.number));
 
     if (canBeReflected || canBeApplied) {
       parameters.forEachParameter((Element parameter) {
         expressions.add(
             js.number(task.metadataEmitter.reifyName(parameter.name)));
         if (backend.mustRetainMetadata) {
           Iterable<int> metadataIndices =
               parameter.metadata.map((MetadataAnnotation annotation) {
             Constant constant =
-                backend.constants.getConstantForMetadata(annotation);
+                backend.constants.getConstantForMetadata(annotation).value;
             backend.constants.addCompileTimeConstantForEmission(constant);
             return task.metadataEmitter.reifyMetadata(annotation);
           });
           expressions.add(
               new jsAst.ArrayInitializer.from(metadataIndices.map(js.number)));
         }
       });
     }
     if (canBeReflected) {
       jsAst.LiteralString reflectionName;
@@ skipping 16 matching lines @@
     jsAst.ArrayInitializer arrayInit =
       new jsAst.ArrayInitializer.from(expressions);
     compiler.dumpInfoTask.registerElementAst(member,
         builder.addProperty(name, arrayInit));
   }
 
   void addMemberField(VariableElement member, ClassBuilder builder) {
     // For now, do nothing.
   }
 }