Move constant systems into their own libraries.

tests/compiler/dart2js/backend_dart/opt_constprop_test.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.
 
 import 'dart:async';
 import '../mock_compiler.dart';
 import 'sexpr_unstringifier.dart';
 import 'package:async_helper/async_helper.dart';
 import "package:expect/expect.dart";
 import 'package:compiler/src/cps_ir/cps_ir_nodes_sexpr.dart';
 import 'package:compiler/src/cps_ir/optimizers.dart';
-import 'package:compiler/src/dart2jslib.dart' as dart2js;
+import 'package:compiler/src/constant_system_dart.dart';
 
 // The tests in this file that ensure that sparse constant propagation on the
 // CPS IR works as expected.
 
 // CP1 represents the following incoming dart code:
 //
 //  int main() {
 //    int i = 1;
 //    int j;
 //    if (i == 1) {
@@ skipping 470 matching lines @@
 /// the stringification of the result against the expected output.
 Future testConstantPropagator(String input, String expectedOutput) {
   final compiler = new MockCompiler.internal(
       emitJavaScript: false,
       enableMinification: false);
   return compiler.init().then((_) {
     final unstringifier = new SExpressionUnstringifier();
     final stringifier   = new SExpressionStringifier();
     final optimizer     = new TypePropagator(
         compiler.types,
-        dart2js.DART_CONSTANT_SYSTEM,
+        DART_CONSTANT_SYSTEM,
         new UnitTypeSystem(),
         compiler.internalError);
 
     final f = unstringifier.unstringify(input);
     optimizer.rewrite(f);
 
     String expected = normalizeSExpr(expectedOutput);
     String actual   = normalizeSExpr(stringifier.visit(f));
 
     Expect.equals(expected, actual);
   });
 }
 
 void main() {
   asyncTest(() => testConstantPropagator(CP1_IN, CP1_OUT));
   asyncTest(() => testConstantPropagator(CP2_IN, CP2_OUT));
   asyncTest(() => testConstantPropagator(CP3_IN, CP3_OUT));
   asyncTest(() => testConstantPropagator(CP4_IN, CP4_OUT));
   asyncTest(() => testConstantPropagator(CP5_IN, CP5_OUT));
   asyncTest(() => testConstantPropagator(CP6_IN, CP6_OUT));
   asyncTest(() => testConstantPropagator(CP7_IN, CP7_OUT));
   asyncTest(() => testConstantPropagator(CP8_IN, CP8_OUT));
   asyncTest(() => testConstantPropagator(CP9_IN, CP9_OUT));
   asyncTest(() => testConstantPropagator(CP10_IN, CP10_OUT));
 }