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}
diff --git a/webrtc/system_wrappers/source/metrics_default_unittest.cc b/webrtc/system_wrappers/source/metrics_default_unittest.cc
index 4ffb4c2..c2eefe5 100644
--- a/webrtc/system_wrappers/source/metrics_default_unittest.cc
+++ b/webrtc/system_wrappers/source/metrics_default_unittest.cc
@@ -8,10 +8,9 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#include "webrtc/test/gtest.h"
-
 #include "webrtc/system_wrappers/include/metrics.h"
 #include "webrtc/system_wrappers/include/metrics_default.h"
+#include "webrtc/test/gtest.h"
 
 namespace webrtc {