Revert "Use relative URIs for core library part-of statements."

sdk/lib/core/symbol.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.
 
-part of "core.dart";
+part of dart.core;
 
 /// Opaque name used by mirrors, invocations and [Function.apply].
 abstract class Symbol {
   /**
    * Constructs a new Symbol.
    *
    * The name must be a valid public Dart member name,
    * public constructor name, or library name, optionally qualified.
    *
    * A qualified name is a valid name preceded by a public identifier name
@@ skipping 28 matching lines @@
   int get hashCode;
 
   /**
    * Symbols are equal to other symbols that correspond to the same member name.
    *
    * Qualified member names, like `#foo.bar` are equal only if they have the
    * same identifiers before the same final member name.
    */
   bool operator ==(other);
 }