Reverts CLs related to the TLAB due to heap exhaustion.

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
diff --git a/runtime/vm/isolate.cc b/runtime/vm/isolate.cc
index c32e7e63451358def58842205b5803762b5a8548..d97a4cfa1548eb9d7058dd4b76b3983f69f2e772 100644
--- a/runtime/vm/isolate.cc
+++ b/runtime/vm/isolate.cc
@@ -2563,6 +2563,10 @@ Thread* Isolate::ScheduleThread(bool is_mutator, bool bypass_safepoint) {
     os_thread->set_thread(thread);
     if (is_mutator) {
       scheduled_mutator_thread_ = thread;
+      if (this != Dart::vm_isolate()) {
+        scheduled_mutator_thread_->set_top(heap()->new_space()->top());
+        scheduled_mutator_thread_->set_end(heap()->new_space()->end());
+      }
     }
     Thread::SetCurrent(thread);
     os_thread->EnableThreadInterrupts();
@@ -2601,6 +2605,12 @@ void Isolate::UnscheduleThread(Thread* thread,
   os_thread->set_thread(NULL);
   OSThread::SetCurrent(os_thread);
   if (is_mutator) {
+    if (this != Dart::vm_isolate()) {
+      heap()->new_space()->set_top(scheduled_mutator_thread_->top_);
+      heap()->new_space()->set_end(scheduled_mutator_thread_->end_);
+    }
+    scheduled_mutator_thread_->top_ = 0;
+    scheduled_mutator_thread_->end_ = 0;
     scheduled_mutator_thread_ = NULL;
   }
   thread->isolate_ = NULL;