webrtc-internals: dont calculate stun rtt in milliseconds

the related standard currentRoundTripTime is defined in seconds:
  https://www.w3.org/TR/webrtc-stats/#dom-rtcicecandidatepairstats-currentroundtriptime
and having the calculated stat on a different timescale is confusing.

BUG=None

Change-Id: Iac04deef1bb0c346c5bd7e08a944764b4c29e845
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2300100Reviewed-by: Henrik Boström <hbos@chromium.org>
Commit-Queue: Philipp Hancke <philipp.hancke@googlemail.com>
Cr-Commit-Position: refs/heads/master@{#803426}

content/browser/resources/media/stats_rates_calculator.js

@@ -512,9 +512,8 @@ class StatsRatesCalculator {
               'bytesReceived', 'timestamp', CalculatorModifier.kBytesToBits),
           // TODO(https://crbug.com/webrtc/10569): Add packetsSent and
           // packetsReceived once implemented.
-          totalRoundTripTime: new RateCalculator(
-              'totalRoundTripTime', 'responsesReceived',
-              CalculatorModifier.kMillisecondsFromSeconds),
+          totalRoundTripTime:
+              new RateCalculator('totalRoundTripTime', 'responsesReceived'),
         },
       },
     ];