Fixes the regression caused by 7568e1f18e.

runtime/vm/isolate.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/isolate.h"
 
 #include "include/dart_api.h"
 #include "include/dart_native_api.h"
 #include "platform/assert.h"
 #include "platform/text_buffer.h"
@@ skipping 2556 matching lines @@
     thread->heap_ = heap();
     thread->set_os_thread(os_thread);
     ASSERT(thread->execution_state() == Thread::kThreadInNative);
     thread->set_execution_state(Thread::kThreadInVM);
     thread->set_safepoint_state(0);
     thread->set_vm_tag(VMTag::kVMTagId);
     ASSERT(thread->no_safepoint_scope_depth() == 0);
     os_thread->set_thread(thread);
     if (is_mutator) {
       mutator_thread_ = thread;
-      if ((Dart::vm_isolate() != NULL) &&
-          (heap() != Dart::vm_isolate()->heap())) {
-        mutator_thread_->set_top(0);
-        mutator_thread_->set_end(0);
-      }
     }
     Thread::SetCurrent(thread);
     os_thread->EnableThreadInterrupts();
   }
   return thread;
 }
 
 void Isolate::UnscheduleThread(Thread* thread,
                                bool is_mutator,
                                bool bypass_safepoint) {
@@ skipping 18 matching lines @@
   if (!bypass_safepoint) {
     // Ensure that the thread reports itself as being at a safepoint.
     thread->EnterSafepoint();
   }
   OSThread* os_thread = thread->os_thread();
   ASSERT(os_thread != NULL);
   os_thread->DisableThreadInterrupts();
   os_thread->set_thread(NULL);
   OSThread::SetCurrent(os_thread);
   if (is_mutator) {
-    if ((Dart::vm_isolate() != NULL) &&
-        (heap() != Dart::vm_isolate()->heap())) {
-      if (mutator_thread_->HasActiveTLAB()) {
-        heap()->AbandonRemainingTLAB(mutator_thread_);
-      }
-    }
-    ASSERT(!mutator_thread_->HasActiveTLAB());
     mutator_thread_ = NULL;
   }
   thread->isolate_ = NULL;
   thread->heap_ = NULL;
   thread->set_os_thread(NULL);
   thread->set_execution_state(Thread::kThreadInNative);
   thread->set_safepoint_state(Thread::SetAtSafepoint(true, 0));
   thread->clear_pending_functions();
   ASSERT(thread->no_safepoint_scope_depth() == 0);
   // Return thread structure.
@@ skipping 218 matching lines @@
 void IsolateSpawnState::DecrementSpawnCount() {
   ASSERT(spawn_count_monitor_ != NULL);
   ASSERT(spawn_count_ != NULL);
   MonitorLocker ml(spawn_count_monitor_);
   ASSERT(*spawn_count_ > 0);
   *spawn_count_ = *spawn_count_ - 1;
   ml.Notify();
 }
 
 }  // namespace dart