mac: use errno instead of return value of pthread_setname_np
mac: use errno instead of return value of pthread_setname_np

It appears the return value is always -1 on error.

BUG=47058

Review URL: http://codereview.chromium.org/2824018

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@50373 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser