Revert "Change some platform libraries to use `part of URI`."

sdk/lib/core/comparable.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.
 
-part of "dart:core";
+part of dart.core;
 
 /**
  * The signature of a generic comparison function.
  *
  * A comparison function represents an ordering on a type of objects.
  * A total ordering on a type means that for two values, either they
  * are equal or one is greater than the other (and the latter must then be
  * smaller than the former).
  *
  * A [Comparator] function represents such a total ordering by returning
@@ skipping 69 matching lines @@
   /**
    * A [Comparator] that compares one comparable to another.
    *
    * It returns the result of `a.compareTo(b)`.
    *
    * This utility function is used as the default comparator
    * for ordering collections, for example in the [List] sort function.
    */
   static int compare(Comparable a, Comparable b) => a.compareTo(b);
 }