Fix rtc::CurrentThreadId() on Android

We have been using the Linux way of getting the thread id on Android,
even though we have a special code path for getting it on Android.

BUG=webrtc:8110

Review-Url: https://codereview.webrtc.org/3001333002
Cr-Original-Commit-Position: refs/heads/master@{#19494}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: d950d9eda1c970d87d0d67c1fd46f06735030438
1 file changed