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

tests/utils/dummy_compiler_test.dart

 // 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.
 // VMOptions=
 // VMOptions=--print-object-histogram
 
 // Smoke test of the dart2js compiler API.
 library dummy_compiler;
 
 import 'dart:async';
 import "package:async_helper/async_helper.dart";
 
 import 'package:compiler/compiler.dart';
 
 import '../compiler/dart2js/mock_libraries.dart';
 
 String libProvider(Uri uri) {
-  if (uri.path.endsWith("/core.dart")) {
+  if (uri.path.endsWith(".platform")) {
+    return DEFAULT_PLATFORM_CONFIG;
+  } if (uri.path.endsWith("/core.dart")) {
     return buildLibrarySource(DEFAULT_CORE_LIBRARY);
   } else if (uri.path.endsWith('core_patch.dart')) {
     return DEFAULT_PATCH_CORE_SOURCE;
   } else if (uri.path.endsWith('interceptors.dart')) {
     return buildLibrarySource(DEFAULT_INTERCEPTORS_LIBRARY);
   } else if (uri.path.endsWith('js_helper.dart')) {
     return buildLibrarySource(DEFAULT_JS_HELPER_LIBRARY);
   } else if (uri.path.endsWith('isolate_helper.dart')) {
     return buildLibrarySource(DEFAULT_ISOLATE_HELPER_LIBRARY);
   } else if (uri.path.endsWith('/async.dart')) {
@@ skipping 31 matching lines @@
               new Uri(scheme: 'package', path: '/'),
               provider, handler);
   result.then((CompilationResult result) {
     if (!result.isSuccess) {
       throw 'Compilation failed';
     }
   }, onError: (e, s) {
       throw 'Compilation failed: $e\n$s';
   }).then(asyncSuccess);
 }