Fixing WebRTC after moving from src/webrtc to src/

In https://webrtc-review.googlesource.com/c/src/+/1560 we moved WebRTC
from src/webrtc to src/ (in order to preserve an healthy git history).
This CL takes care of fixing header guards, #include paths, etc...

NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
TBR=tommi@webrtc.org


Bug: chromium:611808
Change-Id: Iea91618212bee0af16aa3f05071eab8f93706578
Reviewed-on: https://webrtc-review.googlesource.com/1561
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Henrik Kjellander <kjellander@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#19846}
diff --git a/webrtc.gni b/webrtc.gni
index af4d6f9..b36352d 100644
--- a/webrtc.gni
+++ b/webrtc.gni
@@ -205,7 +205,7 @@
 # Templates
 #
 
-# Points to //webrtc/ in webrtc stand-alone or to //third_party/webrtc/ in
+# Points to // in webrtc stand-alone or to //third_party/webrtc/ in
 # chromium.
 # We need absolute paths for all configs in templates as they are shared in
 # different subdirectories.