Reclaim the CreatedFromSnapshot bit and use it to indicate VM Heap object

tests/isolate/message3_test.dart

Index: tests/isolate/message3_test.dart
diff --git a/tests/isolate/message3_test.dart b/tests/isolate/message3_test.dart
index c07a7e68329820d9aa0e660c28e3fb5c4d808b17..4267cee9be3c65e35bcdaa3c4b81bb4c5b9c1e68 100644
--- a/tests/isolate/message3_test.dart
+++ b/tests/isolate/message3_test.dart
@@ -394,7 +394,7 @@ void runTests(SendPort ping, Queue checks) {
     Expect.equals("field", f.field);
     Expect.isFalse(identical(nonConstF, f));
   });
-  checks.add((x) {  // g1.
+  checks.add((x) {  // g2.
     Expect.isTrue(x is G);
     Expect.isFalse(identical(g1, x));
     F f = x.field;
@@ -403,7 +403,7 @@ void runTests(SendPort ping, Queue checks) {
   });
   checks.add((x) {  // g3.
     Expect.isTrue(x is G);
-    Expect.identical(g1, x);  /// constInstance: continued
+    Expect.identical(g3, x);  /// constInstance: continued
     F f = x.field;
     Expect.equals("field", f.field);
     Expect.identical(constF, f);  /// constInstance: continued