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

tests/compiler/dart2js/analyze_only_test.dart

Index: tests/compiler/dart2js/analyze_only_test.dart
diff --git a/tests/compiler/dart2js/analyze_only_test.dart b/tests/compiler/dart2js/analyze_only_test.dart
index 08100a62d3978ba6a09fd660c611730c536e1039..2d771fb53491534f8d476e7f3790e1898f477f68 100644
--- a/tests/compiler/dart2js/analyze_only_test.dart
+++ b/tests/compiler/dart2js/analyze_only_test.dart
@@ -49,8 +49,8 @@ runCompiler(String main, List<String> options,
               localProvider, localHandler, options, outputCollector);
   result.then((_) {
     onValue(outputCollector.getOutput('', 'js'), errors, warnings);
-  }, onError: (e) {
-    throw 'Compilation failed: ${Error.safeToString(e)}';
+  }, onError: (e, st) {
+    throw 'Compilation failed: ${e} ${st}';
   }).then(asyncSuccess).catchError((error, stack) {
     print('\n\n-----------------------------------------------');
     print('main source:\n$main');