Deal with Javascript integer limitations in heap snapshot processing to handle 64-bit target VMs.

runtime/observatory/lib/src/elements/heap_snapshot.dart

Index: runtime/observatory/lib/src/elements/heap_snapshot.dart
diff --git a/runtime/observatory/lib/src/elements/heap_snapshot.dart b/runtime/observatory/lib/src/elements/heap_snapshot.dart
index f75726fb53575aaf905bd661c89e804f3f25581e..1dee104e9242e2ebf921e2fea41dba39082bda34 100644
--- a/runtime/observatory/lib/src/elements/heap_snapshot.dart
+++ b/runtime/observatory/lib/src/elements/heap_snapshot.dart
@@ -75,8 +75,7 @@ class DominatorTreeRow extends TableTreeRow {
     firstColumn.children.add(gap);
 
     AnyServiceRefElement objectRef = new Element.tag("any-service-ref");
-    String hexAddress = vertex.address.toRadixString(16);
-    snapshot.isolate.getObjectByAddress(hexAddress).then((obj) {
+    snapshot.isolate.getObjectByAddress(vertex.address).then((obj) {
       objectRef.ref = obj;
     });
     objectRef.style.alignSelf = 'center';