Rename Constant to ConstantValue and ConstExp to ConstantExpression.

sdk/lib/_internal/compiler/implementation/common.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.
 
 library dart2js.common;
 
 export 'constants/values.dart' show
-    Constant,
-    InterceptorConstant,
-    NullConstant,
-    TypeConstant;
+    ConstantValue,
+    InterceptorConstantValue,
+    NullConstantValue,
+    TypeConstantValue;
 
 export 'dart2jslib.dart' show
     CompilerTask,
     Compiler,
     ConstantEnvironment,
     MessageKind,
     Selector,
     TreeElements,
     invariant;
 
@@ skipping 23 matching lines @@
 
 export 'types/types.dart' show
     TypeMask;
 
 export 'universe/universe.dart' show
     SelectorKind;
 
 export 'util/util.dart' show
     Link,
     SpannableAssertionFailure;