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

runtime/vm/dart_api_impl_test.cc

Index: runtime/vm/dart_api_impl_test.cc
diff --git a/runtime/vm/dart_api_impl_test.cc b/runtime/vm/dart_api_impl_test.cc
index 677bdd615128240316859c9a90a5afcbe3d81e28..1cff1c5205c011e5a313e2c573cd9bf393f740bd 100644
--- a/runtime/vm/dart_api_impl_test.cc
+++ b/runtime/vm/dart_api_impl_test.cc
@@ -2970,8 +2970,8 @@ TEST_CASE(IsolateInterrupt) {
   Isolate::SetInterruptCallback(IsolateInterruptTestCallback);
 
   sync = new Monitor();
-  Thread* thread = new Thread(BusyLoop_start, 0);
-  EXPECT(thread != NULL);
+  ThreadHandle thread = Thread::Start(BusyLoop_start, 0);
+  EXPECT(thread != Thread::kInvalidThreadHandle);
 
   {
     MonitorLocker ml(sync);