bootstat: Fix false metrics due to soft reboots.

Use a flag to enable/disable logging metrics, set to false during soft
reboots.

Bug: 32807863
Change-Id: Ib1359327af4e18d40400c29961c454f7be1b8d0c
Test: None
(cherry picked from commit 800ceb45)

bootstat/bootstat.rc

@@ -11,8 +11,26 @@ on post-fs-data
 on post-fs-data && property:init.svc.bootanim=running
     exec - root root -- /system/bin/bootstat -r post_decrypt_time_elapsed
 
+# sys.logbootcomplete is a signal to enable the bootstat logging mechanism.
+# This signaling is necessary to prevent logging boot metrics after a soft
+# reboot (e.g., adb shell stop && adb shell start).  /proc/uptime is not reset
+# during a soft reboot, which leads to false boot time metrics being reported.
+#
+# The 'on boot' event occurs once per hard boot (device power on), which
+# switches the flag on. If the device performs a soft reboot, the flag is
+# switched off and cannot be switched on until the device hard boots again.
+
+# Enable bootstat logging on boot.
+on boot
+    setprop sys.logbootcomplete 1
+
+# Disable further bootstat logging on a soft reboot. A soft reboot is
+# signaled by the zygote stopping.
+on property:init.svc.zygote=stopping
+    setprop sys.logbootcomplete 0
+
 # Record boot complete metrics.
-on property:sys.boot_completed=1
+on property:sys.boot_completed=1 && property:sys.logbootcomplete=1
     # Record boot_complete and related stats (decryption, etc).
     exec - root root -- /system/bin/bootstat --record_boot_complete