Introduce heap snapshot into Memory Dashboard

runtime/observatory/lib/src/models/repositories/editor.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // 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
 
 part of models;
 
 abstract class EditorRepository {
-  bool get canOpenClass;
+  bool get isAvailable;
 
   Future openClass(IsolateRef isolate, ClassRef clazz);
+  Future openField(IsolateRef isolate, FieldRef clazz);
+  Future openFunction(IsolateRef isolate, FunctionRef clazz);
+  Future openObject(IsolateRef isolate, ObjectRef clazz);
   Future openSourceLocation(IsolateRef isolate, SourceLocation location);
 }