Fixed the bug that fail to run manual tests with w3c js test harness manually.

[xiuqijix]

Reproduce Test Steps:

1.Select the "Dump JSON" checkbox.
2.Click the "Start" Button.
3.Click the "Stop" Button.
4.Click the "Start" Button.
5.Click the "Stop" Button.

Expected Outcome

Display one json result div.

Actual Outcome

Display more than one json result div.

---

This change is 

[hoppipolla-critic-bot]

Critic review: https://critic.hoppipolla.co.uk/r/5770

This is an external review system which you may optionally use for the code review of your pull request.

In order to help critic track your changes, please do not make in-place history rewrites (e.g. via git rebase -i or git commit --amend) when updating this pull request.

[jgraham]

So this is the fix that I don't really understand, from the various fixes you submitted.

[yugang]

@jgraham , the first commit appear here as the second commit which we submitted here to fix the issue depends on the first one, and the first commit already been merged in： #30 , not sure if the github can skip the first commit here automatically? if not, we will only keep the last on here ASAP, thanks

[xiuqijix]

@jgraham , the first commit appear here as the second commit which we submitted here to fix the issue depends on the first one, and the first commit already been merged in： #30 ,I've tested,the github can skip the first commit here automatically. So you can merge #31 #32 #33 ,one by one, thanks.

[jgraham]

Right, but the central issue I have here is that I don't understand what the second commit in this PR is trying to achieve.

[yugang]

@jgraham , some manual tests in MANIFEST.json need be executed after some manual preconditions, but the tests also are using testharness.js, the wpt runner will execute it and get the test result automatically, so we think the runner should avoid to run tests which marked "manual" in MANIFEST.json