Fix some observatory analysis issues.

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';
 
@@ skipping 897 matching lines @@
       var w = vertex[i];
       if (dom[w] != vertex[semi[w]]) {
         dom[w] = dom[dom[w]];
       }
     }
 
     _doms = dom;
   }
 
   void _calculateRetainedSizes() {
-    var N = _N;
     var Nconnected = _Nconnected;
 
     var size = 0;
     var shallowSizes = _shallowSizes;
     var vertex = _vertex;
     var doms = _doms;
 
     // Sum shallow sizes.
     for (var i = 1; i <= Nconnected; i++) {
       var v = vertex[i];
@@ skipping 116 matching lines @@
     var head = _mergedDomHead;
     var next = _mergedDomNext;
     var workStack = new Uint32List(N);
     var workStackTop = 0;
 
     mergeChildrenAndSort(var parent1, var end) {
       assert(parent1 != SENTINEL);
       if (next[parent1] == end) return;
 
       // Find the middle of the list.
-      int cid = cids[parent1];
       int slow = parent1;
       int fast = parent1;
       while (next[fast] != end && next[next[fast]] != end) {
         slow = next[slow];
         fast = next[next[fast]];
       }
 
       int parent2 = next[slow];
 
       assert(parent2 != SENTINEL);
@@ skipping 10 matching lines @@
       // Children moved to parent1.
       head[parent2] = SENTINEL;
     }
 
     // Push root.
     workStack[workStackTop++] = ROOT;
 
     while (workStackTop > 0) {
       var parent = workStack[--workStackTop];
 
-      var prev = SENTINEL;
       var child = head[parent];
       while (child != SENTINEL) {
         // Push child.
         workStack[workStackTop++] = child;
 
         // Find next sibling with a different cid.
         var after = child;
         while (after != SENTINEL && cids[after] == cids[child]) {
           after = next[after];
         }
 
         // From all the siblings between child and after, take their children,
         // merge them and given to child.
         mergeChildrenAndSort(child, after);
 
         child = after;
       }
     }
   }
 }