An isolate created with spawn function doesn't necessarily agree with its parent on the library pri…

runtime/vm/snapshot.cc

Index: runtime/vm/snapshot.cc
diff --git a/runtime/vm/snapshot.cc b/runtime/vm/snapshot.cc
index 427a19600ca2d3b04491b4f9269d60f27b9cc6f9..b7a1b83c5e8e6aa1d04e29462b6fd0e7ea240616 100644
--- a/runtime/vm/snapshot.cc
+++ b/runtime/vm/snapshot.cc
@@ -268,7 +268,7 @@ RawClass* SnapshotReader::ReadClassId(intptr_t object_id) {
     SetReadException("Invalid object found in message.");
   }
   str_ ^= ReadObjectImpl(kAsInlinedObject);
-  cls = library_.LookupClass(str_);
+  cls = library_.LookupClassAllowPrivate(str_);
   if (cls.IsNull()) {
     SetReadException("Invalid object found in message.");
   }
@@ -299,7 +299,7 @@ RawFunction* SnapshotReader::ReadFunctionId(intptr_t object_id) {
     str_ ^= ReadObjectImpl(kAsInlinedObject);
     func ^= library_.LookupLocalFunction(str_);
   } else {
-    cls_ = library_.LookupClass(str_);
+    cls_ = library_.LookupClassAllowPrivate(str_);
     if (cls_.IsNull()) {
       SetReadException("Expected a class name, but found an invalid name.");
     }