metrics: Fix import paths for headers.

This CL fixes the import path to match the Android format.
The libmetrics headers were also moved to include/metrics to make
exporting headers cleaner.

BUG: 22879597

Change-Id: I67d1ac1746cc3560ae4cbddecf97fa48c9dd1480
diff --git a/metrics/timer_test.cc b/metrics/timer_test.cc
index ec6c6bd..b1689bf 100644
--- a/metrics/timer_test.cc
+++ b/metrics/timer_test.cc
@@ -8,9 +8,9 @@
 #include <gmock/gmock.h>
 #include <gtest/gtest.h>
 
-#include "metrics/metrics_library_mock.h"
-#include "metrics/timer.h"
-#include "metrics/timer_mock.h"
+#include "metrics_library_mock.h"
+#include "timer.h"
+#include "timer_mock.h"
 
 using ::testing::_;
 using ::testing::Return;