Expand part declarations in the builtin library python scripts to avoid having to repeat part decla…

sdk/lib/async/async_sources.gypi

Index: sdk/lib/async/async_sources.gypi
diff --git a/sdk/lib/async/async_sources.gypi b/sdk/lib/async/async_sources.gypi
index 7fdd9566ff5881a78c0bc9e6596bd49e1e771b7f..1606d72a586c321a0810c4bf06033bf206c89acf 100644
--- a/sdk/lib/async/async_sources.gypi
+++ b/sdk/lib/async/async_sources.gypi
@@ -6,16 +6,5 @@
 {
   'sources': [
     'async.dart',
-    # The above file needs to be first as it lists the parts below.
-    'async_error.dart',
-    'collection_sink.dart',
-    'deferred_load.dart',
-    'future.dart',
-    'future_impl.dart',
-    'stream.dart',
-    'stream_controller.dart',
-    'stream_impl.dart',
-    'stream_pipe.dart',
-    'timer.dart',
   ],
 }