Round results of multiplying QuicBandwidth and QuicTime::Delta rather than truncating. No behavior…

Round results of multiplying QuicBandwidth and QuicTime::Delta rather than truncating.  No behavior change expected.

This will result in slightly more accurate time calculations, but should
not make any real impact, since we should not be relying on
microsecond-level-precision to that extent.

Chromium bug:
https://bugs.chromium.org/p/chromium/issues/detail?id=640984

Merge internal change: 131334594

R=rch@chromium.org
BUG=

[Victor Vasiliev, 2016-09-03 01:56:56]

The CQ bit was checked by vasilvv@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-09-03 01:57:11]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[Ryan Hamilton, 2016-09-03 02:00:54]

lgtm

[commit-bot: I haz the power, 2016-09-03 02:23:04]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-09-03 02:23:05]

Dry run: Try jobs failed on following builders:
  ios-simulator on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-simulator/bui...)