Fix many warnings/errors when building Observatory

runtime/observatory/tests/observatory_ui/mocks/repositories/heap_snapshot.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 mocks;
 
 class HeapSnapshotLoadingProgressEventMock
     implements M.HeapSnapshotLoadingProgressEvent {
   final M.HeapSnapshotLoadingProgress progress;
 
@@ skipping 20 matching lines @@
 
 typedef Stream<
     M
         .HeapSnapshotLoadingProgressEvent> HeapSnapshotRepositoryMockCallback(
     M.IsolateRef cls, bool gc);
 
 class HeapSnapshotRepositoryMock implements M.HeapSnapshotRepository {
   final HeapSnapshotRepositoryMockCallback _get;
 
   Stream<M.HeapSnapshotLoadingProgressEvent> get(M.IsolateRef isolate,
-      {bool gc: false}) {
+      {M.HeapSnapshotRoots roots: M.HeapSnapshotRoots.vm, bool gc: false}) {
     if (_get != null) {
       return _get(isolate, gc);
     }
     return null;
   }
 
   HeapSnapshotRepositoryMock({HeapSnapshotRepositoryMockCallback getter})
       : _get = getter;
 }