Adding capture device selection capability for video_loopback. It will help to select any capture device to test the utility. In future we can add screen share as capture device.

BUG=webrtc:7719

Change-Id: Iddc66188341c0c90e96766dff671ac3863bf3f5d
Reviewed-on: https://chromium-review.googlesource.com/517523
Commit-Queue: Peter Boström <pbos@webrtc.org>
Reviewed-by: Peter Boström <pbos@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#18392}
diff --git a/AUTHORS b/AUTHORS
index c11e96d..4b387ed 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -46,6 +46,7 @@
 Silviu Caragea <silviu.cpp@gmail.com>
 Stefan Gula <steweg@gmail.com>
 Steve Reid <sreid@sea-to-sky.net>
+Tarun Chawla <trnkumarchawla@gmail.com>
 Vladimir Beloborodov <VladimirTechMan@gmail.com>
 Vicken Simonian <vsimon@gmail.com>
 Victor Costan <costan@gmail.com>