- Remove redundant (and wrong) flushing of store buffers in unit test.

runtime/vm/thread_test.cc

Index: runtime/vm/thread_test.cc
diff --git a/runtime/vm/thread_test.cc b/runtime/vm/thread_test.cc
index 33ce9f83db89e6db6212ac18e146925e1894fbac..f619d51e6ca87de76d8959f6ab8a36f9fb76ae05 100644
--- a/runtime/vm/thread_test.cc
+++ b/runtime/vm/thread_test.cc
@@ -566,11 +566,6 @@ TEST_CASE(HelperAllocAndGC) {
   Monitor done_monitor;
   bool done = false;
   Isolate* isolate = Thread::Current()->isolate();
-  // Flush store buffers, etc.
-  // TODO(koda): Currently, the GC only does this for the current thread, (i.e,
-  // the helper, in this test), but it should be done for all *threads*
-  // while reaching a safepoint.
-  isolate->thread_registry()->PrepareForGC();
   Dart::thread_pool()->Run(new AllocAndGCTask(isolate, &done_monitor, &done));
   {
     while (true) {