Two "overlay_icon" event pings are sent after refreshing a video page

[Softvision-CristinaBadescu]

[Notes]:

• Sometimes this issue is reproducible only at the second refresh of the page.

[Affected versions]:

• Firefox Developer Edition 59.0b9
• Min-Vid Shield Study Onboarding 0.4.7 - Shield Study

[Affected Platforms]:

• All Windows

[Prerequisites]:

• Latest Min-Vid v.0.4.7 Shield Study Onboarding ("active" or "activeAndOnboarding" variant) was previously installed on a clean profile.

[Steps to reproduce]:

1. Open the browser with the profile from prerequisites and navigate to a YouTube song link (eg. https://www.youtube.com/watch?v=oJ18op-kVF0).
2. Send the video to the player.
3. Refresh the page.
4. Go to "about:telemetry" page and observe the event of the ping generated by the refresh action.

[Expected result]:

• One "overlay_icon" event ping is sent.

[Actual result]:

• Two "overlay_icon" event pings are sent.

[Additional notes]:

• This issue is also reproducible if you send videos from homepage or users/channels pages and refresh an already open YouTube song page.
• This issue is reproducible on every song page you visit.
• This issue is also reproducible if you use the "Send to tab" option.
• This issue is reproducible even though you close Min Vid player.
• This issue is not reproducible on YouTube homepage and users/channel pages.
• Here is a screen recording of the issue: https://goo.gl/UsSGRP