Add update reboot metric to the update engine.

This change add the Installer.UpdateNumReboots metric.

This records the number of reboots that occurred while an update was being
attempted. It uses a marker file stored in tmp to discover whether or not
it's already recorded the reboot.

BUG=chromium:226766
TEST=Unittests | ran an update on a test machine and rebooted/resumed and
checked about:histograms to confirm numbers. Also restart update-engine to
verify it didn't double count that.

Change-Id: I5d2af9d5b62a9d974c7c6243a89cb3359051b650
Reviewed-on: https://gerrit.chromium.org/gerrit/47710
Tested-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Chris Sosa <sosa@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
diff --git a/integration_unittest.cc b/integration_unittest.cc
index f42b89e..e54c0e2 100644
--- a/integration_unittest.cc
+++ b/integration_unittest.cc
@@ -7,6 +7,7 @@
 #include <glib.h>
 #include <pthread.h>
 #include <gtest/gtest.h>
+#include "update_engine/constants.h"
 #include "update_engine/download_action.h"
 #include "update_engine/install_action.h"
 #include "update_engine/libcurl_http_fetcher.h"
@@ -134,7 +135,7 @@
   ASSERT_EQ(0, system("rm -f /tmp/update_engine_test_postinst_out.txt"));
   ASSERT_EQ(0, System(string("mkdir -p ") + kTestDir + "/etc"));
   ASSERT_EQ(0, system((string("mkdir -p ") + kTestDir +
-                       utils::kStatefulPartition +
+                       kStatefulPartition +
                        "/etc").c_str()));
   ASSERT_TRUE(WriteFileString(string(kTestDir) + "/etc/lsb-release",
                               "GOOGLE_RELEASE=0.2.0.0\n"