Change typedef of PlatformThreadRef for Fuchsia from pthread_t to zx_handle_t

Bug: webrtc:8893
Change-Id: I748e800f4b100b3bc3646c359e5240507ca0e03d
Tbr: guidou@webrtc.org
Reviewed-on: https://webrtc-review.googlesource.com/54307
Reviewed-by: Tommi <tommi@webrtc.org>
Reviewed-by: Guido Urdaneta <guidou@webrtc.org>
Commit-Queue: Tommi <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22069}
diff --git a/rtc_base/platform_thread_types.h b/rtc_base/platform_thread_types.h
index e6331e7..72aaa4b 100644
--- a/rtc_base/platform_thread_types.h
+++ b/rtc_base/platform_thread_types.h
@@ -28,7 +28,7 @@
 typedef DWORD PlatformThreadRef;
 #elif defined(WEBRTC_FUCHSIA)
 typedef zx_handle_t PlatformThreadId;
-typedef pthread_t PlatformThreadRef;
+typedef zx_handle_t PlatformThreadRef;
 #elif defined(WEBRTC_POSIX)
 typedef pid_t PlatformThreadId;
 typedef pthread_t PlatformThreadRef;