Clear fields sticky_error and pending_functions when unscheduling thread; enable background compila…

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
diff --git a/runtime/vm/isolate.cc b/runtime/vm/isolate.cc
index 70cca1ab368e7c03d20569c3f4be49ce83ecb902..8126882dc38fdcfe146d96424d96c3060e0261e1 100644
--- a/runtime/vm/isolate.cc
+++ b/runtime/vm/isolate.cc
@@ -2603,6 +2603,7 @@ void Isolate::UnscheduleThread(Thread* thread,
   thread->set_os_thread(NULL);
   thread->set_execution_state(Thread::kThreadInVM);
   thread->set_safepoint_state(0);
+  thread->clear_pending_functions();
   ASSERT(thread->no_safepoint_scope_depth() == 0);
   // Return thread structure.
   thread_registry()->ReturnThreadLocked(is_mutator, thread);