Move the thread local functions to the Thread class in runtime/platform

runtime/platform/thread_macos.h

Index: runtime/platform/thread_macos.h
diff --git a/runtime/platform/thread_macos.h b/runtime/platform/thread_macos.h
index c2b30595c15188bbe1e4195650e7fd5108376280..ad185c4a3fdaf6c60294d8205d1717fadeb2746e 100644
--- a/runtime/platform/thread_macos.h
+++ b/runtime/platform/thread_macos.h
@@ -15,6 +15,26 @@
 
 namespace dart {
 
+typedef pthread_key_t ThreadLocalKey;
+
+class ThreadInlineImpl {
+ private:
+  ThreadInlineImpl() {}
+  ~ThreadInlineImpl() {}
+
+  static uword GetThreadLocal(ThreadLocalKey key) {
+    static ThreadLocalKey kUnsetThreadLocalKey = static_cast<pthread_key_t>(-1);
+    ASSERT(key != kUnsetThreadLocalKey);
+    return reinterpret_cast<uword>(pthread_getspecific(key));
+  }
+
+  friend class Thread;
+
+  DISALLOW_ALLOCATION();
+  DISALLOW_COPY_AND_ASSIGN(ThreadInlineImpl);
+};
+
+
 class MutexData {
  private:
   MutexData() {}