GN: Fix webrtc/video/BUILD.gn for Chromium build.

A mistake was made in https://review.webrtc.org/18709004/
so it doesn't build in Chromium. Adding a config to get
the root folder included in the include path solves it.

BUG=3441
TESTED=Local compilation of Chromium's all target with
src/third_party/webrtc linked to the WebRTC checkout with
this CL applied.
TBR=brettw@chromium.org

Review URL: https://webrtc-codereview.appspot.com/19169004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7011 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/webrtc/video/BUILD.gn b/webrtc/video/BUILD.gn
index 121e754..f06d632 100644
--- a/webrtc/video/BUILD.gn
+++ b/webrtc/video/BUILD.gn
@@ -25,6 +25,8 @@
     "video_send_stream.h",
   ]
 
+  configs += [ "..:common_inherited_config" ]
+
   if (is_clang) {
     # Suppress warnings from Chrome's Clang plugins.
     # See http://code.google.com/p/webrtc/issues/detail?id=163 for details.