[vm] Fix reading a named reference to a top-level class.

runtime/vm/snapshot.cc

Index: runtime/vm/snapshot.cc
diff --git a/runtime/vm/snapshot.cc b/runtime/vm/snapshot.cc
index 51e551140aa46197f33016560127835cff4457d3..f54a84c58a77dea8cb372eb5a0375ae106bff456 100644
--- a/runtime/vm/snapshot.cc
+++ b/runtime/vm/snapshot.cc
@@ -276,7 +276,11 @@ RawClass* SnapshotReader::ReadClassId(intptr_t object_id) {
     SetReadException("Invalid object found in message.");
   }
   str_ ^= ReadObjectImpl(kAsInlinedObject);
-  cls = library_.LookupClassAllowPrivate(str_);
+  if (str_.raw() == Symbols::TopLevel().raw()) {
+    cls = library_.toplevel_class();
+  } else {
+    cls = library_.LookupClassAllowPrivate(str_);

[siva, 2017/06/26 20:36:45]

Would it be beneficial to add this login into LookupClassAllowPrivate itself?

[rmacnak, 2017/06/26 20:51:45]

I'm not sure. I don't think we can generally treat library-level lookups as
equivalent to lookups in the corresponding top-level class (I dimly recall that
some top-level members are only added to the library's dictionary and not the
top-level class), so I suspect they usually have to be special-cased anyway.

+  }
   if (cls.IsNull()) {
     SetReadException("Invalid object found in message.");
   }