Use correct FFT scaling for WebAudio AnalyserNode

Use correct FFT scaling for WebAudio AnalyserNode

Currently, for a fixed sine-wave input, the peak FFT amplitude changes
depending on the selected FFT size. This is incorrect; the FFT amplitude
should not appreciably change when the FFT size changes.

Layout test added to verify the FFT result stays approximately constant,
independent of the FFT size used.

When this test is run using an older version of Chrome, the peak varies
from about -44 dB (FFT size 32) to -7 dB (FFT size 2048).  With this CL,
the peak is about -7 dB.  (It's not 0 dB because of the Blackman window that is applied.)

Note: this change may break existing applications that depended on this strange scaling effect.

BUG=341536
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=166687

[Raymond Toy (Google), 2014-02-06 21:44:27]

PTAL.

[Ken Russell (switch to Gerrit), 2014-02-07 02:44:07]

Wow. Nice test for a one-line change. LGTM

[Ken Russell (switch to Gerrit), 2014-02-07 02:44:51]

Note, the BUG= line in the CL description should be the last thing, I think.

[Raymond Toy (Google), 2014-02-07 05:58:49]

On 2014/02/07 02:44:51, Ken Russell wrote:
> Note, the BUG= line in the CL description should be the last thing, I think.

Thanks for the review. I've moved the BUG line to the end as well.

[Raymond Toy (Google), 2014-02-07 05:58:59]

The CQ bit was checked by rtoy@google.com

[commit-bot: I haz the power, 2014-02-07 05:59:10]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rtoy@google.com/156993002/30001

[commit-bot: I haz the power, 2014-02-07 07:33:25]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-02-07 07:33:26]

Commit queue rejected this change because the description was changed
between the time the change entered the commit queue and the time it
was ready to commit. You can safely check the commit box again.

[Raymond Toy (Google), 2014-02-07 07:37:23]

The CQ bit was checked by rtoy@google.com

[commit-bot: I haz the power, 2014-02-07 07:37:40]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rtoy@google.com/156993002/30001

[commit-bot: I haz the power, 2014-02-07 07:38:02]

Change committed as 166687