Rewrite asyncStepOver to use await

runtime/observatory/lib/object_graph.dart

 // Copyright (c) 2014, 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.
 
 library object_graph;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:typed_data';
 
-import 'package:logging/logging.dart';
-
 class _JenkinsSmiHash {
   static int combine(int hash, int value) {
     hash = 0x1fffffff & (hash + value);
     hash = 0x1fffffff & (hash + ((0x0007ffff & hash) << 10));
     return hash ^ (hash >> 6);
   }
 
   static int finish(int hash) {
     hash = 0x1fffffff & (hash + ((0x03ffffff & hash) <<  3));
     hash = hash ^ (hash >> 11);
@@ skipping 469 matching lines @@
       stream.skipUnsigned(); // cid
 
       firstSuccs[id] = edge;
 
       stream.readUnsigned();
       while (!stream.isZero) {
         var childId = addrToId.get(stream.high, stream.mid, stream.low);
         if (childId != null) {
           succs[edge] = childId;
           edge++;
-        } else { 
+        } else {
           // Reference into VM isolate's heap.
         }
         stream.readUnsigned();
       }
       id++;
     }
     firstSuccs[id] = edge; // Extra entry for cheap boundary detection.
 
     assert(id == N + 1);
     assert(edge <= E); // edge is smaller because E was computed before we knew
                        // if references pointed into the VM isolate
 
     _E = edge;
     _firstSuccs = firstSuccs;
     _succs = succs;
   }
 
   void _dfs() {
     var N = _N;
-    var E = _E;
     var firstSuccs = _firstSuccs;
     var succs = _succs;
 
     var stackNodes = new Uint32List(N);
     var stackCurrentEdgePos = new Uint32List(N);
 
     var vertex = new Uint32List(N + 1);
     var semi = new Uint32List(N + 1);
     var parent = new Uint32List(N + 1);
     var dfsNumber = 0;
 
-    var dfsCount = 0;
     var stackTop = 0;
     var root = 1;
 
     // Push root.
     stackNodes[0] = root;
     stackCurrentEdgePos[0] = firstSuccs[root];
 
     while (stackTop >= 0) {
       var v = stackNodes[stackTop];
       var edgePos = stackCurrentEdgePos[stackTop];
@@ skipping 271 matching lines @@
     for (var i = N; i > 1; i--) {
       var v = vertex[i];
       assert(v != 1);
       retainedSizes[doms[i]] += retainedSizes[i];
     }
 
     _retainedSizes = retainedSizes;
     _size = size;
   }
 }