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

runtime/lib/convert_sources.gni

Index: runtime/lib/convert_sources.gni
diff --git a/runtime/lib/convert_sources.gypi b/runtime/lib/convert_sources.gni
similarity index 56%
rename from runtime/lib/convert_sources.gypi
rename to runtime/lib/convert_sources.gni
index 0f3b46b87b20a4a8fe86db748dd3fc873c3d20c6..e37c01725037705b794b64945d7efc4c6eb53c34 100644
--- a/runtime/lib/convert_sources.gypi
+++ b/runtime/lib/convert_sources.gni
@@ -1,9 +1,5 @@
-# Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+# Copyright (c) 2017, 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.
 
-{
-  'sources': [
-    'convert_patch.dart',
-  ],
-}
+convert_runtime_sources = [ "convert_patch.dart" ]