Set thread names to help debugging.

Have our worker threads call pthread_setname_np() on Linux and Android,
so that they can be easily identified in the thread listing of a
debugger.

BUG=2167

Change-Id: If04b1fa630e82da6f40c9c730eb62cf386fc5a0f
diff --git a/av1/decoder/decodeframe.c b/av1/decoder/decodeframe.c
index 6556a9e..ba0f7f2 100644
--- a/av1/decoder/decodeframe.c
+++ b/av1/decoder/decodeframe.c
@@ -3766,6 +3766,7 @@
       ++pbi->num_workers;
 
       winterface->init(worker);
+      worker->thread_name = "aom tile worker";
       if (worker_idx < num_threads - 1 && !winterface->reset(worker)) {
         aom_internal_error(&cm->error, AOM_CODEC_ERROR,
                            "Tile decoder thread creation failed");