Add 'break' and 'clear' commands to Observatory debugger.

runtime/observatory/lib/src/debugger/debugger.dart

Index: runtime/observatory/lib/src/debugger/debugger.dart
diff --git a/tests/language/enum_private_lib.dart b/runtime/observatory/lib/src/debugger/debugger.dart
similarity index 58%
copy from tests/language/enum_private_lib.dart
copy to runtime/observatory/lib/src/debugger/debugger.dart
index c8fb00f6f3f757100cf1daa96a61ead3f92c0f8c..d028c36fa6a83da0da4b1885c963cd0dbea2f67a 100644
--- a/tests/language/enum_private_lib.dart
+++ b/runtime/observatory/lib/src/debugger/debugger.dart
@@ -2,9 +2,10 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-library enum_private_lib;
+part of debugger;
 
-enum Enum2 {
-  _A,
-  _B,
+// TODO(turnidge): Move more of ObservatoryDebugger to this class.
+abstract class Debugger {
+  Isolate get isolate;
+  ServiceMap get stack;
 }