Support for taking full snapshots from 'dart', not just 'dart_bootstrap'.

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index 29c473933d8d086dfeba67be46614f7850eae603..60e35500e4ab80adfbce2746a66d2f1e9fb84e4a 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -10676,7 +10676,10 @@ void Library::AllocatePrivateKey() const {
   OS::SNPrint(private_key, sizeof(private_key),
               "%c%" Pd "%06" Pd "",
               kPrivateKeySeparator, sequence_value, hash_value);
-  StorePointer(&raw_ptr()->private_key_, String::New(private_key, Heap::kOld));
+  const String& key = String::Handle(zone, String::New(private_key,
+                                                       Heap::kOld));
+  key.Hash();  // This string may end up in the VM isolate.
+  StorePointer(&raw_ptr()->private_key_, key.raw());
 }