Reflection on generics.

runtime/lib/mirrors_impl.dart

Index: runtime/lib/mirrors_impl.dart
diff --git a/runtime/lib/mirrors_impl.dart b/runtime/lib/mirrors_impl.dart
index 5fb76c7c6bf92029ba1a117eb97ee0ec31daaa6c..8bd1f7f0a1795ddbbb05319f14265fefdcd99a12 100644
--- a/runtime/lib/mirrors_impl.dart
+++ b/runtime/lib/mirrors_impl.dart
@@ -501,9 +501,12 @@ class _LocalClassMirrorImpl extends _LocalObjectMirrorImpl
     return _typeVariables;
   }
 
+  Map<Symbol, TypeMirror> _typeArguments = null;
   Map<Symbol, TypeMirror> get typeArguments {
-    throw new UnimplementedError(
-        'ClassMirror.typeArguments is not implemented');
+    if(_typeArguments == null) {
+      _typeArguments = _computeTypeArguments(_reflectee);
+    }
+    return _typeArguments;
   }
 
   bool get isOriginalDeclaration {
@@ -595,6 +598,9 @@ class _LocalClassMirrorImpl extends _LocalObjectMirrorImpl
 
   static _ClassMirror_type_variables(reflectee)
       native "ClassMirror_type_variables";
+
+  static _computeTypeArguments(reflectee)
+      native "ClassMirror_type_arguments";
 }
 
 class _LocalFunctionTypeMirrorImpl extends _LocalClassMirrorImpl