Use metric#time instead of computing duration locally.

Fix a bug in the metric that called 'milliseconds' 1_000_000 for a
multiplier when it should be 1000.

Fixes #5472

logstash-core/lib/logstash/filter_delegator.rb

@@ -37,9 +37,9 @@ module LogStash
     def multi_filter(events)
       @metric_events.increment(:in, events.size)
 
-      start = Time.now
+      clock = @filter.metric.time(:duration_in_millis)
       new_events = @filter.multi_filter(events)
-      @filter.metric.increment(:duration_in_millis, ((Time.now - start)*1000).to_i)
+      clock.stop
 
       # There is no garantee in the context of filter
       # that EVENTS_INT == EVENTS_OUT, see the aggregates and

logstash-core/lib/logstash/instrument/metric.rb

@@ -46,7 +46,7 @@ module LogStash module Instrument
     end
 
     def report_time(namespace, key, duration)
-      collector.push(namespace, key, :mean, :increment, duration)
+      collector.push(namespace, key, :counter, :increment, duration)
     end
 
     # This method return a metric instance tied to a specific namespace
@@ -81,7 +81,7 @@ module LogStash module Instrument
     #
     # @see LogStash::Instrument::Metric#time
     class TimedExecution
-      MILLISECONDS = 1_000_000.0.freeze
+      MILLISECONDS = 1_000.0.freeze
 
       def initialize(metric, namespace, key)
         @metric = metric