init start time tracking.

With this change, init sets a property "init.start" to show the
CLOCK_BOOTTIME time at which init itself started, and for each service
an "init.svc.<name>.start" property to show the CLOCK_BOOTTIME time at
which that service was most recently started.

These times can be used by tools like bootstat to track boot time.

As part of this change, move init over to std::chrono. Also, rather than
make the command-line argument handling more complex, I've switched to
using an environment variable for communication between first- and
second-stage init, and added another environment variable to pass the
start time of the first stage through to the second stage.

Bug: http://b/32780225
Test: manual
Change-Id: Ia65a623e1866ea688b9a5433d6507926ce301dfe
diff --git a/init/service.h b/init/service.h
index d9e8f57..013e65f 100644
--- a/init/service.h
+++ b/init/service.h
@@ -30,6 +30,7 @@
 #include "descriptors.h"
 #include "init_parser.h"
 #include "keyword_map.h"
+#include "util.h"
 
 #define SVC_DISABLED       0x001  // do not autostart with class
 #define SVC_ONESHOT        0x002  // do not restart on exit
@@ -75,7 +76,7 @@
     void Stop();
     void Terminate();
     void Restart();
-    void RestartIfNeeded(time_t& process_needs_restart);
+    void RestartIfNeeded(time_t* process_needs_restart_at);
     bool Reap();
     void DumpState() const;
 
@@ -134,9 +135,9 @@
 
     unsigned flags_;
     pid_t pid_;
-    time_t time_started_;    // time of last start
-    time_t time_crashed_;    // first crash within inspection window
-    int nr_crashed_;         // number of times crashed within window
+    boot_clock::time_point time_started_; // time of last start
+    boot_clock::time_point time_crashed_; // first crash within inspection window
+    int crash_count_;                     // number of times crashed within window
 
     uid_t uid_;
     gid_t gid_;