metrics: Fixes a comment for |TimerReporter::ReportMilliseconds|.

It turns out that |TimerReporter::ReportMilliseconds| does report a value
for a timer that hasn't been started (in shill,
|Metrics::NotifyDevice*Finished| calls |Stop| immediately before
|ReportMilliseconds| and it works just fine.  This is perfectly OK, it's
just that the comment didn't reflect this.  This CL fixes that.

BUG=None.
TEST=None.

Change-Id: I578d554106acdb92957bfe0197622a1054cfa9c9
Reviewed-on: https://gerrit.chromium.org/gerrit/46337
Reviewed-by: Darin Petkov <petkov@chromium.org>
Reviewed-by: Wade Guthrie <wdg@chromium.org>
Tested-by: Wade Guthrie <wdg@chromium.org>
Commit-Queue: Wade Guthrie <wdg@chromium.org>
diff --git a/metrics/timer.h b/metrics/timer.h
index 1d31976..e80950c 100644
--- a/metrics/timer.h
+++ b/metrics/timer.h
@@ -111,8 +111,7 @@
   }
 
   // Reports the current duration to UMA, in milliseconds. Returns false if
-  // there is nothing to report, i.e. the timer was not started or a metrics
-  // library is not set.
+  // there is nothing to report, e.g. a metrics library is not set.
   virtual bool ReportMilliseconds() const;
 
   // Accessor methods.