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

sdk/lib/vmservice/running_isolates.dart

Index: sdk/lib/vmservice/running_isolates.dart
diff --git a/sdk/lib/vmservice/running_isolates.dart b/sdk/lib/vmservice/running_isolates.dart
index 2b6c15c079eec4fd417dc8f12dc5f27039539314..daf4442c3160e8b09f45eb30c64b820f8fe8c905 100644
--- a/sdk/lib/vmservice/running_isolates.dart
+++ b/sdk/lib/vmservice/running_isolates.dart
@@ -2,7 +2,7 @@
 // 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:_vmservice";
+part of dart._vmservice;
 
 class RunningIsolates implements MessageRouter {
   final Map<int, RunningIsolate> isolates = new Map<int, RunningIsolate>();