Add OSThread::GetCurrentThreadTraceId and use it in the timeline implementation

runtime/vm/timeline.cc

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include <cstdlib>
 
 #include "vm/atomic.h"
 #include "vm/isolate.h"
 #include "vm/json_stream.h"
 #include "vm/lockers.h"
@@ skipping 322 matching lines @@
   }
 }
 
 
 void TimelineEvent::Init(EventType event_type,
                          const char* label) {
   ASSERT(label != NULL);
   set_event_type(event_type);
   timestamp0_ = 0;
   timestamp1_ = 0;
-  thread_ = OSThread::GetCurrentThreadId();
+  thread_ = OSThread::GetCurrentThreadTraceId();
   isolate_ = Isolate::Current();
   label_ = label;
   FreeArguments();
 }
 
 
 void TimelineEvent::PrintJSON(JSONStream* stream) const {
   JSONObject obj(stream);
   int64_t pid = OS::ProcessId();
   int64_t tid = OSThread::ThreadIdToIntPtr(thread_);
@@ skipping 640 matching lines @@
 
 
 TimelineEventBlock* TimelineEventBlockIterator::Next() {
   ASSERT(current_ != NULL);
   TimelineEventBlock* r = current_;
   current_ = current_->next();
   return r;
 }
 
 }  // namespace dart