TaskScheduler: Adjust shutdown behavior of delayed tasks.

base/task_scheduler/task.h

Index: base/task_scheduler/task.h
diff --git a/base/task_scheduler/task.h b/base/task_scheduler/task.h
index 2b53c690fddffc752ce63ec98b900a0b34f06674..7d9f9f4e5ba6cc79bff166c24f2230a4d511f14d 100644
--- a/base/task_scheduler/task.h
+++ b/base/task_scheduler/task.h
@@ -24,11 +24,13 @@ namespace internal {
 struct BASE_EXPORT Task : public PendingTask {
   // |posted_from| is the site the task was posted from. |task| is the closure
   // to run. |traits| is metadata about the task. |delay| is a delay that must
-  // expire before the Task runs.
+  // expire before the Task runs. If |delay| is non-zero and the shutdown
+  // behavior in |traits| is BLOCK_SHUTDOWN, the shutdown behavior is
+  // automatically changed to SKIP_ON_SHUTDOWN.
   Task(const tracked_objects::Location& posted_from,
        const Closure& task,
        const TaskTraits& traits,
-       const TimeDelta& delay);
+       TimeDelta delay);

[gab, 2016/09/30 19:01:26]

Is passing TimeDelta by value common practice? I know it's fine in practice
because it's merely an int64_t but style is usually still to pass classes by
const&.

[fdoray, 2016/09/30 19:10:11]

See https://cs.chromium.org/chromium/src/base/time/time.h?l=24
TaskRunner takes a TimeDelta by value.

[robliao, 2016/09/30 19:16:56]

I don't think there is a style ruling on passing by reference vs by value. The
only requirement is if you pass by reference, you make it a const reference.

There is a strong convention that generally input args are const reference, but
not absolutely required.

In these cases, I sometimes let the code vote, and it looks like TimeDelta (by
value) wins.

[gab, 2016/09/30 19:34:45]

IMO by value only wins because of
https://cs.chromium.org/chromium/src/base/time/time.h?l=24. i.e. only if the
class provides documented guarantees, otherwise you can't assume it won't grow
beyond POD types only and become inefficient to pass by value.

   ~Task();
 
   // The TaskTraits of this task.