[Mac] In PlatformThread::CurrentId(), use pthread_self() instead of mach_thread_self().

base/threading/platform_thread.h

Index: base/threading/platform_thread.h
diff --git a/base/threading/platform_thread.h b/base/threading/platform_thread.h
index f958ef6c7db61f09ec7a55bb513b275592b0b241..4d4a06c01368a9c5b1c8c0cadd5b154ebfffc533 100644
--- a/base/threading/platform_thread.h
+++ b/base/threading/platform_thread.h
@@ -19,12 +19,8 @@
 #include <windows.h>
 #elif defined(OS_POSIX)
 #include <pthread.h>
-#if defined(OS_MACOSX)
-#include <mach/mach.h>
-#else  // OS_POSIX && !OS_MACOSX
 #include <unistd.h>
 #endif
-#endif
 
 namespace base {
 
@@ -39,12 +35,8 @@ const PlatformThreadHandle kNullThreadHandle = NULL;
 #elif defined(OS_POSIX)
 typedef pthread_t PlatformThreadHandle;
 const PlatformThreadHandle kNullThreadHandle = 0;
-#if defined(OS_MACOSX)
-typedef mach_port_t PlatformThreadId;
-#else  // OS_POSIX && !OS_MACOSX
 typedef pid_t PlatformThreadId;
 #endif
-#endif
 
 const PlatformThreadId kInvalidThreadId = 0;