Update comment in byte_stream.h to not mention BrowserThread::FILE

R=avi@chromium.org

Bug: 689520
Change-Id: If26b672ce68f8362c8f9194597720199f094ca30
Reviewed-on: https://chromium-review.googlesource.com/587890
Commit-Queue: Avi Drissman <avi@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#489985}
1 file changed