Move constant systems into their own libraries.

pkg/compiler/lib/src/mirrors_used.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.mirrors_used;
 
+import 'compile_time_constants.dart' show
+    ConstantCompiler;
 import 'constants/expressions.dart';
 import 'constants/values.dart' show
     ConstantValue,
     ConstructedConstantValue,
     ListConstantValue,
     StringConstantValue,
     TypeConstantValue;
 
 import 'dart_types.dart' show
     DartType,
     InterfaceType,
     TypeKind;
 
 import 'dart2jslib.dart' show
     Compiler,
     CompilerTask,
-    ConstantCompiler,
     MessageKind,
     TreeElements,
     invariant;
 
 import 'elements/elements.dart' show
     ClassElement,
     Element,
     LibraryElement,
     MetadataAnnotation,
     ScopeContainerElement,
@@ skipping 553 matching lines @@
       // @MirrorsUsed(targets: fisk)
       //                       ^^^^
       //
       // Instead of saying 'fisk' should pretty print the problematic constant
       // value.
       return spannable;
     }
     return node;
   }
 }