[Isolates] Fix Linux build in Isolates branch.

src/v8threads.cc

 // Copyright 2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 323 matching lines @@
 #ifdef ENABLE_DEBUGGER_SUPPORT
   isolate_->debug()->FreeThreadResources();
 #endif
   isolate_->stack_guard()->FreeThreadResources();
   isolate_->regexp_stack()->FreeThreadResources();
   isolate_->bootstrapper()->FreeThreadResources();
 }
 
 
 bool ThreadManager::IsArchived() {
-  return Isolate::CurrentPerIsolateThreadData()->thread_state() != NULL;
+  Isolate::PerIsolateThreadData* data = Isolate::CurrentPerIsolateThreadData();
+  return data != NULL && data->thread_state() != NULL;
 }
 
 
 void ThreadManager::Iterate(ObjectVisitor* v) {
   // Expecting no threads during serialization/deserialization
   for (ThreadState* state = FirstThreadStateInUse();
        state != NULL;
        state = state->Next()) {
     char* data = state->data();
     data = HandleScopeImplementer::Iterate(v, data);
@@ skipping 107 matching lines @@
 // Acknowledge the preemption by the receiving thread.
 void ContextSwitcher::PreemptionReceived() {
   ASSERT(Locker::IsLocked());
   // There is currently no accounting being done for this. But could be in the
   // future, which is why we leave this in.
 }
 
 
 }  // namespace internal
 }  // namespace v8