Removes dartc reliance on its own libraries, now can be targeted at any implementation's libraries

compiler/lib/implementation/core.dart

-// Copyright (c) 2011, 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.
-
-class ConstHelper {
-  static String getConstId(var o) native;
-
-  static String getConstMapId(Map map) native {
-    StringBuffer sb = new StringBuffer();
-    sb.add("m");
-    bool first = true;
-    for (String key in map.getKeys()) {
-      if (first) {
-        first = false;
-      } else {
-        sb.add(",");
-      }
-      sb.add(getConstId(key));
-      sb.add(",");
-      sb.add(getConstId(map[key]));
-    }
-    return sb.toString();
-  }
-}
-
-class ExceptionHelper {
-  static NullPointerException createNullPointerException() native {
-    return new NullPointerException();
-  }
-
-  static ObjectNotClosureException createObjectNotClosureException() native {
-    return new ObjectNotClosureException();
-  }
-
-  static NoSuchMethodException createNoSuchMethodException(
-      receiver, functionName, arguments) native {
-    return new NoSuchMethodException(receiver, functionName, arguments);
-  }
-
-  static TypeError createTypeError(String srcType, String dstType) native {
-    return new TypeError(srcType, dstType);
-  }
-  
-  static AssertionError createAssertionError() native {
-    return new AssertionError();
-  }
-}
-
-class _CoreJsUtil {
-  static Map _newMapLiteral() native {
-    return new LinkedHashMap();
-  }
-}
-