Add comments explaining Task Manager idle wakeups computation.

base/process/process_metrics.cc

Index: base/process/process_metrics.cc
diff --git a/base/process/process_metrics.cc b/base/process/process_metrics.cc
index cc6532c8dca15c233044c24c4f5e0e3557ef99db..a38930a208857b6c914f51f84170b1eae7f6c5ea 100644
--- a/base/process/process_metrics.cc
+++ b/base/process/process_metrics.cc
@@ -84,8 +84,9 @@ int ProcessMetrics::CalculateIdleWakeupsPerSecond(
   last_idle_wakeups_time_ = time;
   last_absolute_idle_wakeups_ = absolute_idle_wakeups;
 
-  // Round to average wakeups per second.
   int64_t wakeups_delta_for_ms = wakeups_delta * Time::kMicrosecondsPerSecond;
+  // Round the result up by adding 1/2 (the second term resolves to 1/2 without
+  // dropping down into floating point).

[brucedawson, 2017/02/02 19:52:03]

It's funny how the set of idioms that are obvious and not needing explanation
varies between programmers. I agree that this one is non-obvious to enough
readers to justify a more specific comment.

   return (wakeups_delta_for_ms + time_delta / 2) / time_delta;
 }
 #else