feat(dart/transform): Track timing of transform tasks

modules_dart/transform/test/transform/common/recording_logger.dart

@@ -0,0 +1,33 @@
+library angular2.test.transform.common.read_file;
+
+import 'package:barback/barback.dart';
+import 'package:code_transformers/messages/build_logger.dart';
+import 'package:source_span/source_span.dart';
+
+class RecordingLogger implements BuildLogger {
+  @override
+  final String detailsUri = '';
+  @override
+  final bool convertErrorsToWarnings = false;
+
+  bool hasErrors = false;
+
+  List<String> logs = [];
+
+  void _record(prefix, msg) => logs.add('$prefix: $msg');
+
+  void info(msg, {AssetId asset, SourceSpan span}) => _record('INFO', msg);
+
+  void fine(msg, {AssetId asset, SourceSpan span}) => _record('FINE', msg);
+
+  void warning(msg, {AssetId asset, SourceSpan span}) => _record('WARN', msg);
+
+  void error(msg, {AssetId asset, SourceSpan span}) {
+    hasErrors = true;
+    _record('ERROR', msg);
+  }
+
+  Future writeOutput() => throw new UnimplementedError();
+  Future addLogFilesFromAsset(AssetId id, [int nextNumber = 1]) =>
+      throw new UnimplementedError();
+}