Introduce "CommonElements"

tests/compiler/dart2js/type_combination_test.dart

 // Copyright (c) 2012, 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 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'package:compiler/src/js_backend/backend_helpers.dart';
 import 'package:compiler/src/js_backend/js_backend.dart';
 import 'package:compiler/src/types/types.dart';
 import 'package:compiler/src/world.dart';
@@ skipping 750 matching lines @@
         compiler.enqueuer.resolution,
         compiler.globalDependencies);
     backend.registerInstantiatedType(
         patternImplClass.rawType,
         compiler.enqueuer.resolution,
         compiler.globalDependencies);
     compiler.world.populate();
 
     // Grab hold of a supertype for String so we can produce potential
     // string types.
-    patternClass = compiler.coreLibrary.find('Pattern');
+    patternClass = compiler.commonElements.coreLibrary.find('Pattern');
 
     nonPrimitive1 = new TypeMask.nonNullSubtype(
         compiler.coreClasses.mapClass, world);
     nonPrimitive2 = new TypeMask.nonNullSubtype(
         compiler.coreClasses.functionClass, world);
     potentialArray = new TypeMask.subtype(
         compiler.coreClasses.listClass, world);
     potentialString = new TypeMask.subtype(patternClass, world);
     jsInterceptor = new TypeMask.nonNullSubclass(helpers.jsInterceptorClass,
         world);
@@ skipping 40 matching lines @@
     Expect.notEquals(jsStringOrNull, potentialString,
         "potentialString expected not to be exact JSString");
     Expect.notEquals(jsArrayOrNull, potentialArray,
         "potentialArray expected not to be JSArray subclass");
 
     testUnion(compiler);
     testIntersection(compiler);
     testRegressions(compiler);
   });
 }