Do not allow creation of signature classes in the background compilation path until we have the fix…

runtime/vm/flow_graph_optimizer.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/flow_graph_optimizer.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
 #include "vm/compiler.h"
 #include "vm/cpu.h"
@@ skipping 207 matching lines @@
 
   if (all_cids_known) {
     const Class& receiver_class = Class::Handle(Z,
         isolate()->class_table()->At(class_ids[0]));
     if (!receiver_class.is_finalized()) {
       // Do not eagerly finalize classes. ResolveDynamicForReceiverClass can
       // cause class finalization, since callee's receiver class may not be
       // finalized yet.
       return false;
     }
+    // Do not run the optimization below if in background compilation since
+    // resolution of method extractor functions may create new signature
+    // classes.
+    // TODO(regis): Remove test for background compilation once signature
+    // classes are not generated any longer.
+    if (!thread()->IsMutatorThread()) {
+      return false;
+    }
     const Array& args_desc_array = Array::Handle(Z,
         ArgumentsDescriptor::New(call->ArgumentCount(),
                                  call->argument_names()));
     ArgumentsDescriptor args_desc(args_desc_array);
     const Function& function = Function::Handle(Z,
         Resolver::ResolveDynamicForReceiverClass(
             receiver_class,
             call->function_name(),
             args_desc));
     if (function.IsNull()) {
@@ skipping 8612 matching lines @@
 
   // Insert materializations at environment uses.
   for (intptr_t i = 0; i < exits_collector_.exits().length(); i++) {
     CreateMaterializationAt(
         exits_collector_.exits()[i], alloc, *slots);
   }
 }
 
 
 }  // namespace dart