shill: Log boot statistics for service state changes.

BUG=chromium-os:30169
TEST=unit tests, booted device, /tmp/disk-network-ready is populated

Change-Id: I8f0de3d3f9da2f73ca10977d46262fbbbbd56584
Reviewed-on: https://gerrit.chromium.org/gerrit/25084
Tested-by: Darin Petkov <petkov@chromium.org>
Reviewed-by: Thieu Le <thieule@chromium.org>
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Commit-Ready: Darin Petkov <petkov@chromium.org>
diff --git a/metrics.h b/metrics.h
index aa1493f..bcd1276 100644
--- a/metrics.h
+++ b/metrics.h
@@ -291,6 +291,7 @@
   scoped_ptr<chromeos_metrics::Timer> time_online_timer_;
   scoped_ptr<chromeos_metrics::Timer> time_to_drop_timer_;
   scoped_ptr<chromeos_metrics::Timer> time_resume_to_ready_timer_;
+  bool collect_bootstats_;
 
   DISALLOW_COPY_AND_ASSIGN(Metrics);
 };