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}

test/gtest.h

diff --git a/test/gtest.h b/test/gtest.h
index 886e7b8..928ec49 100644
--- a/test/gtest.h
+++ b/test/gtest.h
@@ -8,10 +8,10 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef WEBRTC_TEST_GTEST_H_
-#define WEBRTC_TEST_GTEST_H_
+#ifndef TEST_GTEST_H_
+#define TEST_GTEST_H_
 
-#include "webrtc/rtc_base/ignore_wundef.h"
+#include "rtc_base/ignore_wundef.h"
 
 RTC_PUSH_IGNORING_WUNDEF()
 #include "testing/gtest/include/gtest/gtest.h"
@@ -24,4 +24,4 @@
 #define GTEST_HAS_DEATH_TEST 0
 #endif
 
-#endif  // WEBRTC_TEST_GTEST_H_
+#endif  // TEST_GTEST_H_