No, osc-*sweep.html and periodicwave-contexts.html don't need to be reverted.  They don't use finishAudioTest; the tests compare the actual and expected wave files for closeness.

No, audiobuffersource-detune-modulation and audiobuffersource-playbackrate-modulation don't actually use finishAudioTest to verify results.  The tests manually compare the actual results with the expected results which are loaded from a file.

finishAudioTest is used in task (that isn't run) to generate the expected result.  Thus, it's not used in the test.

Instead of reverting, add support to save a reference file when run in the browser.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9d77b75aa9748aa22b1136823e0e4d1ace6afd6e

commit 9d77b75aa9748aa22b1136823e0e4d1ace6afd6e
Author: rtoy <rtoy@chromium.org>
Date: Fri Mar 03 22:46:43 2017

Add support creating and saving a new reference file.

Since many tests switched from using finishAudioTest to doing a manual
comparison between the actual results and the expected results in a
wav file, we lost the ability to create easily the reference wav file.

This adds a simple method to allow saving the actual result to a
file.  This is intended to be run in a browser where the actual result
is automatically downloaded for the developer to examine.  This is part
of the test, so it's automatic. When run as a layout test, no file is saved.

This has no effect on the layout tests, so each affected test was
run manually in a browser to see that the file was generated and a
quick check was done comparing the new result with the expected result.

For the record on a linux machine:

detune-modulation: max error 1 bit, 95 differences.
playback-modulation: max error 1 bit, 15 differences.
gain: no differences
webm-decode: max error 1 bit, 465 differences
osc-custom: no differences
osc-sawtooth: no differences
osc-sine: no differences
osc-square: no differences
osc-triangle: no differences

BUG= 696773 
TEST=none

Review-Url: https://codereview.chromium.org/2728613003
Cr-Commit-Position: refs/heads/master@{#454693}

[modify] https://crrev.com/9d77b75aa9748aa22b1136823e0e4d1ace6afd6e/third_party/WebKit/LayoutTests/webaudio/AudioBufferSource/audiobuffersource-detune-modulation.html
[modify] https://crrev.com/9d77b75aa9748aa22b1136823e0e4d1ace6afd6e/third_party/WebKit/LayoutTests/webaudio/AudioBufferSource/audiobuffersource-playbackrate-modulation.html
[modify] https://crrev.com/9d77b75aa9748aa22b1136823e0e4d1ace6afd6e/third_party/WebKit/LayoutTests/webaudio/Gain/gain.html
[modify] https://crrev.com/9d77b75aa9748aa22b1136823e0e4d1ace6afd6e/third_party/WebKit/LayoutTests/webaudio/codec-tests/webm/webm-decode.html
[modify] https://crrev.com/9d77b75aa9748aa22b1136823e0e4d1ace6afd6e/third_party/WebKit/LayoutTests/webaudio/resources/audit-util.js
[modify] https://crrev.com/9d77b75aa9748aa22b1136823e0e4d1ace6afd6e/third_party/WebKit/LayoutTests/webaudio/resources/oscillator-testing.js