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/modules/audio_mixer/audio_frame_manipulator.h b/modules/audio_mixer/audio_frame_manipulator.h
index 20b66ca..fe87169 100644
--- a/modules/audio_mixer/audio_frame_manipulator.h
+++ b/modules/audio_mixer/audio_frame_manipulator.h
@@ -8,10 +8,10 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef WEBRTC_MODULES_AUDIO_MIXER_AUDIO_FRAME_MANIPULATOR_H_
-#define WEBRTC_MODULES_AUDIO_MIXER_AUDIO_FRAME_MANIPULATOR_H_
+#ifndef MODULES_AUDIO_MIXER_AUDIO_FRAME_MANIPULATOR_H_
+#define MODULES_AUDIO_MIXER_AUDIO_FRAME_MANIPULATOR_H_
 
-#include "webrtc/modules/include/module_common_types.h"
+#include "modules/include/module_common_types.h"
 
 namespace webrtc {
 
@@ -27,4 +27,4 @@
 
 }  // namespace webrtc
 
-#endif  // WEBRTC_MODULES_AUDIO_MIXER_AUDIO_FRAME_MANIPULATOR_H_
+#endif  // MODULES_AUDIO_MIXER_AUDIO_FRAME_MANIPULATOR_H_