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/omaha_response_handler_action_unittest.cc b/omaha_response_handler_action_unittest.cc
index 88ac0c4..cb27f82 100644
--- a/omaha_response_handler_action_unittest.cc
+++ b/omaha_response_handler_action_unittest.cc
@@ -240,12 +240,12 @@
   const string kTestDir = "omaha_response_handler_action-test";
   ASSERT_EQ(0, System(string("mkdir -p ") + kTestDir + "/etc"));
   ASSERT_EQ(0, System(string("mkdir -p ") + kTestDir +
-                        utils::kStatefulPartition + "/etc"));
+                      kStatefulPartition + "/etc"));
   ASSERT_TRUE(WriteFileString(
       kTestDir + "/etc/lsb-release",
       "CHROMEOS_RELEASE_TRACK=canary-channel\n"));
   ASSERT_TRUE(WriteFileString(
-      kTestDir + utils::kStatefulPartition + "/etc/lsb-release",
+      kTestDir + kStatefulPartition + "/etc/lsb-release",
       "CHROMEOS_IS_POWERWASH_ALLOWED=true\n"
       "CHROMEOS_RELEASE_TRACK=stable-channel\n"));
 
@@ -277,12 +277,12 @@
   const string kTestDir = "omaha_response_handler_action-test";
   ASSERT_EQ(0, System(string("mkdir -p ") + kTestDir + "/etc"));
   ASSERT_EQ(0, System(string("mkdir -p ") + kTestDir +
-                        utils::kStatefulPartition + "/etc"));
+                      kStatefulPartition + "/etc"));
   ASSERT_TRUE(WriteFileString(
       kTestDir + "/etc/lsb-release",
       "CHROMEOS_RELEASE_TRACK=stable-channel\n"));
   ASSERT_TRUE(WriteFileString(
-      kTestDir + utils::kStatefulPartition + "/etc/lsb-release",
+      kTestDir + kStatefulPartition + "/etc/lsb-release",
       "CHROMEOS_RELEASE_TRACK=canary-channel\n"));
 
   MockSystemState mock_system_state;