It looks like double tap and scrubbing works correctly on macOS. Doing a bit of debugging it looks like the tests are taking too long to perform the second tap. 

[14118:775:0102/083836.360567:ERROR:MediaControlOverlayPlayButtonElement.cpp(186)] "pointerover"
[14118:775:0102/083836.360669:ERROR:MediaControlsImpl.cpp(1047)] "pointerover"
[14118:775:0102/083836.360740:ERROR:MediaControlOverlayPlayButtonElement.cpp(186)] "mouseover"
[14118:775:0102/083836.360754:ERROR:MediaControlsImpl.cpp(1047)] "mouseover"
[14118:775:0102/083836.360767:ERROR:MediaControlOverlayPlayButtonElement.cpp(186)] "pointerdown"
[14118:775:0102/083836.360780:ERROR:MediaControlOverlayPlayButtonElement.cpp(186)] "mousedown"
[14118:775:0102/083836.411191:ERROR:MediaControlOverlayPlayButtonElement.cpp(186)] "pointerup"
[14118:775:0102/083836.411249:ERROR:MediaControlOverlayPlayButtonElement.cpp(186)] "mouseup"
[14118:775:0102/083836.411422:ERROR:MediaControlOverlayPlayButtonElement.cpp(186)] "click" <- tap one
[14118:775:0102/083836.411668:ERROR:MediaControlOverlayPlayButtonElement.cpp(219)] tap timer
[14118:775:0102/083836.699649:ERROR:MediaControlOverlayPlayButtonElement.cpp(186)] "pointerdown"
[14118:775:0102/083836.699707:ERROR:MediaControlOverlayPlayButtonElement.cpp(186)] "mousedown"
[14118:775:0102/083836.715677:ERROR:MediaControlOverlayPlayButtonElement.cpp(262)] timer fired <- timeout for double tap
[14118:775:0102/083836.720406:ERROR:MediaControlOverlayPlayButtonElement.cpp(186)] "pointerup"
[14118:775:0102/083836.720465:ERROR:MediaControlOverlayPlayButtonElement.cpp(186)] "mouseup"
[14118:775:0102/083836.720482:ERROR:MediaControlOverlayPlayButtonElement.cpp(186)] "click" <- tap two
[14118:775:0102/083836.720709:ERROR:MediaControlOverlayPlayButtonElement.cpp(219)] tap timer
[14118:775:0102/083837.020850:ERROR:MediaControlOverlayPlayButtonElement.cpp(262)] timer fired

 Issue 799137  has been merged into this issue.

 Issue 874866  has been merged into this issue.