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/sdk/objc/Framework/UnitTests/RTCSessionDescriptionTest.mm b/sdk/objc/Framework/UnitTests/RTCSessionDescriptionTest.mm
index a6b9f8a..4428153 100644
--- a/sdk/objc/Framework/UnitTests/RTCSessionDescriptionTest.mm
+++ b/sdk/objc/Framework/UnitTests/RTCSessionDescriptionTest.mm
@@ -10,7 +10,7 @@
 
 #import <Foundation/Foundation.h>
 
-#include "webrtc/rtc_base/gunit.h"
+#include "rtc_base/gunit.h"
 
 #import "NSString+StdString.h"
 #import "RTCSessionDescription+Private.h"