Changes new space allocation from simple bump pointer allocation from

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
diff --git a/runtime/vm/isolate.cc b/runtime/vm/isolate.cc
index 8589373d6fda2de551c70ceb77942a4a4ae4c2b7..b7bd9659ea991d3cdcc50b5c8657f6da10b8d05d 100644
--- a/runtime/vm/isolate.cc
+++ b/runtime/vm/isolate.cc
@@ -2574,9 +2574,10 @@ Thread* Isolate::ScheduleThread(bool is_mutator, bool bypass_safepoint) {
     os_thread->set_thread(thread);
     if (is_mutator) {
       mutator_thread_ = thread;
-      if (this != Dart::vm_isolate()) {
-        mutator_thread_->set_top(heap()->new_space()->top());
-        mutator_thread_->set_end(heap()->new_space()->end());
+      if ((Dart::vm_isolate() != NULL) &&
+          (heap() != Dart::vm_isolate()->heap())) {
+        mutator_thread_->set_top(0);
+        mutator_thread_->set_end(0);
       }
     }
     Thread::SetCurrent(thread);
@@ -2617,11 +2618,13 @@ void Isolate::UnscheduleThread(Thread* thread,
   OSThread::SetCurrent(os_thread);
   if (is_mutator) {
     if (this != Dart::vm_isolate()) {
-      heap()->new_space()->set_top(mutator_thread_->top_);
-      heap()->new_space()->set_end(mutator_thread_->end_);
+      // Ensure the new space is pointing right after the last object allocated.
+      if (mutator_thread_->HasActiveTLAB()) {
+        heap()->new_space()->set_top(mutator_thread_->top());
+      }
     }
-    mutator_thread_->top_ = 0;
-    mutator_thread_->end_ = 0;
+    mutator_thread_->set_top(0);
+    mutator_thread_->set_end(0);
     mutator_thread_ = NULL;
   }
   thread->isolate_ = NULL;