pkg/docgen: moved model classes into minilibs

pkg/docgen/lib/src/models/mirror_based.dart

Index: pkg/docgen/lib/src/models/mirror_based.dart
diff --git a/pkg/docgen/lib/src/models/mirror_based.dart b/pkg/docgen/lib/src/models/mirror_based.dart
new file mode 100644
index 0000000000000000000000000000000000000000..fd33bd02d59efb5434ac16b33c46a73ce2982304
--- /dev/null
+++ b/pkg/docgen/lib/src/models/mirror_based.dart
@@ -0,0 +1,13 @@
+library docgen.models.mirror_based;
+
+import '../exports/source_mirrors.dart';
+
+/// Docgen representation of an item to be documented, that wraps around a
+/// dart2js mirror.
+abstract class MirrorBased<TMirror extends DeclarationMirror> {
+  /// The original dart2js mirror around which this object wraps.
+  TMirror get mirror;
+
+  /// Return an informative [Object.toString] for debugging.
+  String toString() => "${super.toString()} - $mirror";
+}