hongchan said he'll take a look at the messy tests.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0e7af755c6ff3377abb22925f319c8cfb699461d

commit 0e7af755c6ff3377abb22925f319c8cfb699461d
Author: hongchan <hongchan@chromium.org>
Date: Thu Feb 16 17:49:21 2017

Refactor decode-audio-data-basic.html to use testharness

- Replace js-test and old Audit with testharness and new Audit.
- Promisefied file loader |Audit.loadFileAtUrl(fileUrl)| is added.
- Refactored complex promise/callback code.
- should().beResolved() now bypassing its argument to the next promise.

For the first pass, I focused on preserving the test behavior. If this looks good,
I will move on to the clean-up and more refactoring.

BUG= 688064 
TEST=
LayoutTests/webaudio/decodeAudioData/decode-audio-data-basic.html

Review-Url: https://codereview.chromium.org/2697733004
Cr-Commit-Position: refs/heads/master@{#451011}

[delete] https://crrev.com/74feab800a38e1cc133c3406d19f966844881e42/third_party/WebKit/LayoutTests/webaudio/decodeAudioData/decode-audio-data-basic-expected.txt
[modify] https://crrev.com/0e7af755c6ff3377abb22925f319c8cfb699461d/third_party/WebKit/LayoutTests/webaudio/decodeAudioData/decode-audio-data-basic.html
[modify] https://crrev.com/0e7af755c6ff3377abb22925f319c8cfb699461d/third_party/WebKit/LayoutTests/webaudio/resources/audit.js