Introduce "platform configurations" to replace categories and libraries.dart.

sdk/lib/dart2dart.platform

Index: sdk/lib/dart2dart.platform
diff --git a/sdk/lib/dart2dart.platform b/sdk/lib/dart2dart.platform
new file mode 100644
index 0000000000000000000000000000000000000000..fd9d8ed0d9d547fbcb3e156a04293704a0d28392
--- /dev/null
+++ b/sdk/lib/dart2dart.platform
@@ -0,0 +1,48 @@
+# Copyright (c) 2015, 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.
+
+# The platform when compiling with dart2js for dart2dart.
+#
+# Includes the _mirror_helpers private libraries
+
+[dart-spec]
+spec:3rd edition.
+
+[features]
+# No extra features.
+
+[libraries]
+async: async/async.dart
+_chrome: _chrome/dart2js/chrome_dart2js.dart
+collection: collection/collection.dart
+convert: convert/convert.dart
+core: core/core.dart
+developer: developer/developer.dart
+html: html/dart2js/html_dart2js.dart
+html_common: html/html_common/html_common_dart2js.dart
+indexed_db: indexed_db/dart2js/indexed_db_dart2js.dart
+io: io/io.dart
+isolate: isolate/isolate.dart
+js: js/dart2js/js_dart2js.dart
+math: math/math.dart
+mirrors: mirrors/mirrors.dart
+nativewrappers: html/dart2js/nativewrappers.dart
+typed_data: typed_data/typed_data.dart
+_native_typed_data: _internal/js_runtime/lib/native_typed_data.dart
+svg: svg/dart2js/svg_dart2js.dart
+web_audio: web_audio/dart2js/web_audio_dart2js.dart
+web_gl: web_gl/dart2js/web_gl_dart2js.dart
+web_sql: web_sql/dart2js/web_sql_dart2js.dart
+_internal: internal/internal.dart
+_js_helper: _internal/js_runtime/lib/js_helper.dart
+_interceptors: _internal/js_runtime/lib/interceptors.dart
+_foreign_helper: _internal/js_runtime/lib/foreign_helper.dart
+_isolate_helper: _internal/js_runtime/lib/isolate_helper.dart
+_js_mirrors: _internal/js_runtime/lib/js_mirrors.dart
+_js_names: _internal/js_runtime/lib/js_names.dart
+_js_primitives: _internal/js_runtime/lib/js_primitives.dart
+_mirror_helper: _internal/js_runtime/lib/mirror_helper.dart
+_js_embedded_names: _internal/js_runtime/lib/shared/embedded_names.dart
+_async_await_error_codes: _internal/js_runtime/lib/shared/async_await_error_codes.dart
+_metadata: html/html_common/metadata.dart