Use a message loop of type UI on the main thread of video-capture service

AVFoundation calls made by the video-capture service on its main thread
require a CFRunLoop which is provided by a UI message loop.
This fixes a number of regressions related to detection of plugged/unplugged
devices that appeared when the default message loops on Mac were changed from
CFRunLoop to Default.

Bug: 834581
Change-Id: If565f400e52407c2f71e32f93e9472556051bad1
Reviewed-on: https://chromium-review.googlesource.com/1049931
Reviewed-by: Robert Sesek <[email protected]>
Reviewed-by: John Abd-El-Malek <[email protected]>
Commit-Queue: Guido Urdaneta <[email protected]>
Cr-Commit-Position: refs/heads/master@{#557202}
diff --git a/chrome/browser/DEPS b/chrome/browser/DEPS
index fc9672c..3a4018e 100644
--- a/chrome/browser/DEPS
+++ b/chrome/browser/DEPS
@@ -78,6 +78,7 @@
   "+services/ui/common",
   "+services/ui/public",
   "+services/ui/service.h",
+  "+services/video_capture/public",
   "+services/viz/privileged",
   "+skia/ext",
   "+third_party/boringssl/src/include",