sync: make scheduling logic and job ownership more obvious.

sync/engine/sync_scheduler.h

Index: sync/engine/sync_scheduler.h
diff --git a/sync/engine/sync_scheduler.h b/sync/engine/sync_scheduler.h
index b9c1ed32c6dd0fd6057d3164326a0f84e4014030..46731929d37d88071a4b4a0e6284454a2291451c 100644
--- a/sync/engine/sync_scheduler.h
+++ b/sync/engine/sync_scheduler.h
@@ -85,13 +85,18 @@ class SyncScheduler : public sessions::SyncSession::Delegate {
 
   // The meat and potatoes. Both of these methods will post a delayed task
   // to attempt the actual nudge (see ScheduleNudgeImpl).
+  // NOTE: |desired_delay| is best-effort. If a nudge is already scheduled to
+  // depart earlier than Now() + delay, the scheduler can and will prefer to
+  // batch the two so that only one nudge is sent (at the earlier time). Also,
+  // as always with delayed tasks and timers, it's possible the task gets run
+  // any time after |desired_delay|.
   virtual void ScheduleNudgeAsync(
-      const base::TimeDelta& delay,
+      const base::TimeDelta& desired_delay,
       NudgeSource source,
       ModelTypeSet types,
       const tracked_objects::Location& nudge_location) = 0;
   virtual void ScheduleNudgeWithStatesAsync(
-      const base::TimeDelta& delay, NudgeSource source,
+      const base::TimeDelta& desired_delay, NudgeSource source,
       const ModelTypeInvalidationMap& invalidation_map,
       const tracked_objects::Location& nudge_location) = 0;