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}

rtc_base/gtest_prod_util.h

diff --git a/rtc_base/gtest_prod_util.h b/rtc_base/gtest_prod_util.h
index 4837604..dc9679f 100644
--- a/rtc_base/gtest_prod_util.h
+++ b/rtc_base/gtest_prod_util.h
@@ -8,8 +8,8 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef WEBRTC_RTC_BASE_GTEST_PROD_UTIL_H_
-#define WEBRTC_RTC_BASE_GTEST_PROD_UTIL_H_
+#ifndef RTC_BASE_GTEST_PROD_UTIL_H_
+#define RTC_BASE_GTEST_PROD_UTIL_H_
 
 // Define our own version of FRIEND_TEST here rather than including
 // gtest_prod.h to avoid depending on any part of GTest in production code.
@@ -35,4 +35,4 @@
   FRIEND_TEST_WEBRTC(test_case_name, FLAKY_##test_name); \
   FRIEND_TEST_WEBRTC(test_case_name, FAILS_##test_name)
 
-#endif  // WEBRTC_RTC_BASE_GTEST_PROD_UTIL_H_
+#endif  // RTC_BASE_GTEST_PROD_UTIL_H_