Set the stack base value for thread pool threads at the start so that profile ticks for threads sho…

runtime/vm/thread_pool.cc

Index: runtime/vm/thread_pool.cc
diff --git a/runtime/vm/thread_pool.cc b/runtime/vm/thread_pool.cc
index 70bac99675bfd66b65c0e53418dea7ae99caf57d..fb0f7d7c69b2fac5d7d1af0843eaa2e08c87500f 100644
--- a/runtime/vm/thread_pool.cc
+++ b/runtime/vm/thread_pool.cc
@@ -433,6 +433,9 @@ void ThreadPool::Worker::Main(uword args) {
   ThreadJoinId join_id = os_thread->join_id();
   ThreadPool* pool;
 
+  // Set the thread's stack_base based on the current stack pointer.
+  os_thread->set_stack_base(Thread::GetCurrentStackPointer());
+
   {
     MonitorLocker ml(&worker->monitor_);
     ASSERT(worker->task_);