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

runtime/vm/os_thread.h

 // Copyright (c) 2012, 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.
 
 #ifndef VM_OS_THREAD_H_
 #define VM_OS_THREAD_H_
 
 #include "platform/globals.h"
 #include "vm/globals.h"
 
@@ skipping 30 matching lines @@
 
   // NOTE: Destructor currently ignored on Windows (issue 23474).
   static ThreadLocalKey CreateThreadLocal(ThreadDestructor destructor = NULL);
   static void DeleteThreadLocal(ThreadLocalKey key);
   static uword GetThreadLocal(ThreadLocalKey key) {
     return ThreadInlineImpl::GetThreadLocal(key);
   }
   static void SetThreadLocal(ThreadLocalKey key, uword value);
   static intptr_t GetMaxStackSize();
   static ThreadId GetCurrentThreadId();
+  static ThreadId GetCurrentThreadTraceId();
   static intptr_t CurrentCurrentThreadIdAsIntPtr() {
     return ThreadIdToIntPtr(GetCurrentThreadId());
   }
   static ThreadJoinId GetCurrentThreadJoinId();
   static void Join(ThreadJoinId id);
   static intptr_t ThreadIdToIntPtr(ThreadId id);
   static ThreadId ThreadIdFromIntPtr(intptr_t id);
   static bool Compare(ThreadId a, ThreadId b);
   static void GetThreadCpuUsage(ThreadId thread_id, int64_t* cpu_usage);
 };
@@ skipping 51 matching lines @@
   MonitorData data_;  // OS-specific data.
 
   DISALLOW_COPY_AND_ASSIGN(Monitor);
 };
 
 
 }  // namespace dart
 
 
 #endif  // VM_OS_THREAD_H_