QA/Fennec/Presentation API

Please take notice that this is a very rough draft, with some bullet points for future work

Bugzilla: https://bugzilla.mozilla.org/show_bug.cgi?id=1184036

Testplan:

• Run w3c test cases (include all tests from http://w3c-test.org/presentation-api/)
• Run a smoke test on Shih-Chiang Chien’s build (verify that the new bugs regressed from presentation API = check vs latest nightly)
• Monitor crash-rate (check with schien to have crash reporter enabled on his build)
• Until then, check adb logcat
• Monitor power consumption (schien’s build vs latest nightly)
• https://developer.android.com/studio/profile/battery-historian.html

Test run for http://w3c-test.org/presentation-api/controlling-ua/ : https://docs.google.com/spreadsheets/d/1uub8yabL0-_7TUaBPZ7sbhqYNcn936IYQSU6vNhMULY/edit#gid=2140443213

Concerns: Bug 1313368 - [Presentation API] Fennec stalls when trying to load a page