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

tests/compiler/dart2js/categories_test.dart

 // 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.
 
 import "package:expect/expect.dart";
 import 'package:async_helper/async_helper.dart';
 
 import "memory_compiler.dart";
 
 runTest(String source, String categories, int expectedErrors) async {
   var collector = new DiagnosticCollector();
   await runCompiler(
       memorySourceFiles: {"main.dart": source},
       options: ["--categories=$categories"],
       diagnosticHandler: collector);
   Expect.equals(expectedErrors, collector.errors.length);
   Expect.equals(0, collector.warnings.length);
 }
 
 void main() {
   asyncTest(() async {
-    await runTest("import 'dart:async'; main() {}", "Embedded", 1);
     await runTest("import 'dart:async'; main() {}", "Client", 0);
     await runTest("import 'dart:async'; main() {}", "Server", 0);
-    await runTest("import 'dart:html'; main() {}", "Embedded", 1);
     await runTest("import 'dart:html'; main() {}", "Client", 0);
     await runTest("import 'dart:html'; main() {}", "Server", 1);
-    await runTest("import 'dart:io'; main() {}", "Embedded", 1);
     await runTest("import 'dart:io'; main() {}", "Client", 1);
     await runTest("import 'dart:io'; main() {}", "Server", 0);
-    await runTest("import 'dart:_internal'; main() {}", "Embedded", 2);
-    await runTest("import 'dart:_internal'; main() {}", "Client", 2);
-    await runTest("import 'dart:_internal'; main() {}", "Server", 2);
+    await runTest("import 'dart:_internal'; main() {}", "Client", 1);
+    await runTest("import 'dart:_internal'; main() {}", "Server", 1);
   });
 }