Minor work for background compilation

runtime/vm/class_table.cc

 // Copyright (c) 2012, 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/class_table.h"
 #include "vm/flags.h"
 #include "vm/freelist.h"
 #include "vm/growable_array.h"
 #include "vm/heap.h"
 #include "vm/object.h"
@@ skipping 126 matching lines @@
              top_);
     }
     cls.set_id(top_);
     table_[top_] = cls.raw();
     top_++;  // Increment next index.
   }
 }
 
 
 void ClassTable::RegisterAt(intptr_t index, const Class& cls) {
+  ASSERT(Thread::Current()->IsMutatorThread());
   ASSERT(index != kIllegalCid);
   ASSERT(index >= kNumPredefinedCids);
   if (index >= capacity_) {
     // Grow the capacity of the class table.
     // TODO(koda): Add ClassTable::Grow to share code.
     intptr_t new_capacity = index + capacity_increment_;
     if (!Class::is_valid_id(index) || new_capacity < capacity_) {
       FATAL1("Fatal error in ClassTable::Register: invalid index %" Pd "\n",
              index);
     }
@@ skipping 384 matching lines @@
 
 void ClassTable::UpdateLiveNew(intptr_t cid, intptr_t size) {
   ClassHeapStats* stats = PreliminaryStatsAt(cid);
   ASSERT(stats != NULL);
   ASSERT(size >= 0);
   stats->post_gc.AddNew(size);
 }
 
 
 }  // namespace dart