Use fractional numbers when recording media viewing time

[jasonrsadler]

Description

Current viewing time for youtube videos is recording by saving the viewing time as int when the time reporting interval comes in. This can result in the gain or loss of seconds to the actual viewing time.

Steps to Reproduce

1. Open youtube videos
2. Compare viewing times with recorded viewing times

Actual result:

Viewing times recorded can on occasion be off by multiple seconds from what the actual viewing time is

Expected result:

Viewing time recorded should closely match the actual viewing time

Reproduces how often:

Brave version (chrome://version info)

Brave	0.57.1 Chromium: 70.0.3538.35 (Developer Build) (64-bit)
Revision	28dcb499844fa40c28d5f62e337876cb936f79f5-refs/branch-heads/3538@{#678}
OS	Mac OS X

Reproducible on current release:

Yes

Website problems only:

• Does the issue resolve itself when disabling Brave Shields?
• Is the issue reproducible on the latest version of Chrome?

Additional Information

cc @NejcZdovc

[Miyayes]

@zenparsing Is this possibly resolved by your recent work on A-C measurement?