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/timer.cc b/metrics/timer.cc
index 90948b5..dd78425 100644
--- a/metrics/timer.cc
+++ b/metrics/timer.cc
@@ -2,13 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "timer.h"
+#include "metrics/timer.h"
 
 #include <string>
 
 #include <base/memory/scoped_ptr.h>
 
-#include "metrics_library.h"
+#include "metrics/metrics_library.h"
 
 namespace chromeos_metrics {