Sort #includes that got unsorted when gmock.h and gtest.h moved to webrtc/test/

gmock.h and gtest.h were moved (or rather, got wrappers so that we
could put some icky compatibility hacks in one place instead of 500)
in this CL: https://codereview.webrtc.org/2358993004/

NOPRESUBMIT=true
BUG=webrtc:6398

Review-Url: https://codereview.webrtc.org/2381013002
Cr-Commit-Position: refs/heads/master@{#14464}

webrtc/modules/audio_coding/test/opus_test.cc

@@ -14,7 +14,6 @@
 
 #include <string>
 
-#include "webrtc/test/gtest.h"
 #include "webrtc/common_types.h"
 #include "webrtc/engine_configurations.h"
 #include "webrtc/modules/audio_coding/codecs/opus/opus_interface.h"
@@ -22,6 +21,7 @@
 #include "webrtc/modules/audio_coding/test/TestStereo.h"
 #include "webrtc/modules/audio_coding/test/utility.h"
 #include "webrtc/system_wrappers/include/trace.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/test/testsupport/fileutils.h"
 
 namespace webrtc {