Change the thread interface in runtime/platform and use it starting all threads

runtime/vm/message_queue_test.cc

Index: runtime/vm/message_queue_test.cc
diff --git a/runtime/vm/message_queue_test.cc b/runtime/vm/message_queue_test.cc
index e807b32d38ee70c48ce079d52326e2f2c5b17c07..8d6fba181a95b8cd001c9165a6626e39b1dc0da9 100644
--- a/runtime/vm/message_queue_test.cc
+++ b/runtime/vm/message_queue_test.cc
@@ -109,8 +109,8 @@ void MessageReceiver_start(uword unused) {
 TEST_CASE(MessageQueue_WaitNotify) {
   sync = new Monitor();
 
-  Thread* thread = new Thread(MessageReceiver_start, 0);
-  EXPECT(thread != NULL);
+  ThreadHandle thread = Thread::Start(MessageReceiver_start, 0);
+  EXPECT(thread != Thread::kInvalidThreadHandle);
 
   // Wait for the shared queue to be created.
   while (shared_queue == NULL) {