Add a manual test for providing a stable state in alert/confirm/prompt

https://www.w3.org/Bugs/Public/show_bug.cgi?id=24707
Update the stable state in dialogs test to match spec change

http://html5.org/r/8620
gzip trickle test response data should be large enough to ensure we get multiple HTTP packets
make sure progress event assertation only runs once, better comments
Test the metadata used for createHTMLDocument().
Merge the -baseline and -additional tests for Selectors API level 1.
Remove the baseline/additional split from selectors.js.
Remove trailing whitespace.
Move the selectors-api tests to dom, where they now belong.
Check disabled-video at next frame

If test checks pixels of video element at same frame, video element has
privious frame not blackness, because video element wasn't rederred after track
was disabled.
Add a manual test for providing a stable state in print()

Gecko currently fails this test.
Whitelist gifs from the CR-at-EOL lint check.
Merge pull request #1174 from Ms2ger/cr-gif

Whitelist gifs from the CR-at-EOL lint check.
Merge pull request #1115 from w3c/hallvors/gzipfix2

improve test for gzip and progress events; r=zcorpan
Add a manual test for providing a stable state in beforeunload
Merge pull request #970 from foolip/stable-state-alert

Add a manual test for providing a stable state in alert/confirm/prompt
Remove trailing whitespace.
Replace tabs by spaces.
Merge pull request #1167 from Ms2ger/selectors

Cleanup the querySelector{,All} tests; r=MikeSmith+jgraham
Merge pull request #1173 from isairz/track-disable

Check disabled-video at next frame