Add LibraryMirror.declarations and ClassMirror.declarations to the API and both implementations.

tests/lib/mirrors/stringify.dart

Index: tests/lib/mirrors/stringify.dart
diff --git a/tests/lib/mirrors/stringify.dart b/tests/lib/mirrors/stringify.dart
index 369f2c130c403bef81b88ca2e1445fce4bab240c..364bdcff7285af3f53120e857d7e0f69a4ed048b 100644
--- a/tests/lib/mirrors/stringify.dart
+++ b/tests/lib/mirrors/stringify.dart
@@ -105,6 +105,7 @@ stringifyClass(ClassMirror cls) {
 stringifyMethod(MethodMirror method) {
   var buffer = new StringBuffer();
   writeDeclarationOn(method, buffer);
+  if (method.isAbstract) buffer.write(', abstract');
   if (method.isStatic) buffer.write(', static');
   if (method.isGetter) buffer.write(', getter');
   if (method.isSetter) buffer.write(', setter');