Improve mobile Safari PWA support in demo.
Improve mobile Safari PWA support in demo.

Closes #2143

Change-Id: Ic0b1963ef0f040b637136b71255b7e4527e3985b

tvoli/shaka-player,tvoli/shaka-player,tvoli/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player