Update includes for webrtc/{base => rtc_base} rename (2/3)

I used a command like this to update the paths:
perl -pi -e "s/webrtc\/base/webrtc\/rtc_base/g" `find webrtc/rtc_base -name "*.cc" -o -name "*.h"`

BUG=webrtc:7634
NOPRESUBMIT=True # cpplint errors that aren't caused by this CL.

Review-Url: https://codereview.webrtc.org/2969623003
Cr-Commit-Position: refs/heads/master@{#18870}
diff --git a/webrtc/system_wrappers/source/metrics_default.cc b/webrtc/system_wrappers/source/metrics_default.cc
index 6ca90da..f9a6f6a 100644
--- a/webrtc/system_wrappers/source/metrics_default.cc
+++ b/webrtc/system_wrappers/source/metrics_default.cc
@@ -11,8 +11,8 @@
 
 #include <algorithm>
 
-#include "webrtc/base/criticalsection.h"
-#include "webrtc/base/thread_annotations.h"
+#include "webrtc/rtc_base/criticalsection.h"
+#include "webrtc/rtc_base/thread_annotations.h"
 #include "webrtc/system_wrappers/include/metrics.h"
 
 // Default implementation of histogram methods for WebRTC clients that do not