Reland "Merge more Kernel infrastructure from kernel_sdk SDK fork."

runtime/lib/mirrors_sources.gypi

 # Copyright (c) 2011, 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.
 
 # Implementation sources.
 
 {
   'sources': [
     'mirrors.cc',
     'mirrors.h',
+    # mirrors_patch.dart needs to be the first dart file because it contains
+    # imports.
     'mirrors_patch.dart',
     'mirrors_impl.dart',
     'mirror_reference.dart',
   ],
 }