[infra] Translate _sources.gypi files to _sources.gni files

runtime/lib/isolate_sources.gypi

Index: runtime/lib/isolate_sources.gypi
diff --git a/runtime/lib/isolate_sources.gypi b/runtime/lib/isolate_sources.gypi
deleted file mode 100644
index d54fadfb52ec666fe915b4f2b51f9b00c916ed76..0000000000000000000000000000000000000000
--- a/runtime/lib/isolate_sources.gypi
+++ /dev/null
@@ -1,12 +0,0 @@
-# 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.
-
-# This file contains all sources for the dart:isolate library.
-{
-  'sources': [
-    'isolate_patch.dart',
-    'isolate.cc',
-    'timer_impl.dart',
-  ],
-}