Avoid trusting the length encoded in the Snapshot if there is an

runtime/vm/dart.cc

Index: runtime/vm/dart.cc
===================================================================
--- runtime/vm/dart.cc	(revision 11409)
+++ runtime/vm/dart.cc	(working copy)
@@ -141,11 +141,15 @@
     // Initialize from snapshot (this should replicate the functionality
     // of Object::Init(..) in a regular isolate creation path.
     Object::InitFromSnapshot(isolate);
+
+    // TODO(turnidge): Remove once length is not part of the snapshot.
     const Snapshot* snapshot = Snapshot::SetupFromBuffer(snapshot_buffer);
+    ASSERT(snapshot->kind() == Snapshot::kFull);
     if (FLAG_trace_isolates) {
       OS::Print("Size of isolate snapshot = %ld\n", snapshot->length());
     }
-    SnapshotReader reader(snapshot, isolate);
+    SnapshotReader reader(snapshot->content(), snapshot->length(),
+                          Snapshot::kFull, isolate);
     reader.ReadFullSnapshot();
     if (FLAG_trace_isolates) {
       isolate->heap()->PrintSizes();