metrics: fix lint warnings

This CL solve the cros lint warnings.
This is mostly due to:
* header guards
* include path
* few google style guide warnings

BUG=chromium:389229
TEST=FEATURES=test emerge-amd64-generic metrics

Change-Id: Ibbfcd2c88926bcc0c1ce9275b4ad0fb0748cd4de
Reviewed-on: https://chromium-review.googlesource.com/207248
Reviewed-by: Bertrand Simonnet <bsimonnet@chromium.org>
Commit-Queue: Bertrand Simonnet <bsimonnet@chromium.org>
Tested-by: Bertrand Simonnet <bsimonnet@chromium.org>
Reviewed-by: Luigi Semenzato <semenzato@chromium.org>
diff --git a/metrics/persistent_integer.cc b/metrics/persistent_integer.cc
index d4ef8b2..3020f7b 100644
--- a/metrics/persistent_integer.cc
+++ b/metrics/persistent_integer.cc
@@ -2,14 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "persistent_integer.h"
+#include "metrics/persistent_integer.h"
 
 #include <fcntl.h>
 
 #include <base/logging.h>
 #include <base/posix/eintr_wrapper.h>
 
-#include "metrics_library.h"
+#include "metrics/metrics_library.h"
 
 namespace {