As an example of how much CPU a-rate biquads actually use, see  issue 813504 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/59636b605b8e4b382a58a4bd8827a3a06d1df42d

commit 59636b605b8e4b382a58a4bd8827a3a06d1df42d
Author: Raymond Toy <rtoy@chromium.org>
Date: Tue Apr 24 02:26:20 2018

Implement selectable AudioParam rate

AudioParam has a new attribute, automationRate, to allow the user to choose whether
the AudioParam is "a-rate" or "k-rate".  Add support for setting and getting
the attribute.

Update all AudioParams to support a-rate and k-rate when allowed.

Spec: https://webaudio.github.io/web-audio-api/#dom-audioparam-automationrate
Intent: https://groups.google.com/a/chromium.org/d/msg/blink-dev/extLjVzLw7s/9XUZvQqcBQAJ

Bug:  828947 
Change-Id: Ibb9fe8bc0dedf3cfdcf33727734b5d66e5a7ca2f
Reviewed-on: https://chromium-review.googlesource.com/945076
Commit-Queue: Raymond Toy <rtoy@chromium.org>
Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552965}
[add] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/WebKit/LayoutTests/external/wpt/webaudio/the-audio-api/the-audioparam-interface/automation-rate-testing.js
[add] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/WebKit/LayoutTests/external/wpt/webaudio/the-audio-api/the-audioparam-interface/automation-rate.html
[add] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/WebKit/LayoutTests/external/wpt/webaudio/the-audio-api/the-audioparam-interface/k-rate-audioworklet.https.html
[add] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/WebKit/LayoutTests/external/wpt/webaudio/the-audio-api/the-audioparam-interface/k-rate-biquad.html
[add] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/WebKit/LayoutTests/external/wpt/webaudio/the-audio-api/the-audioparam-interface/k-rate-constant-source.html
[add] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/WebKit/LayoutTests/external/wpt/webaudio/the-audio-api/the-audioparam-interface/k-rate-delay.html
[add] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/WebKit/LayoutTests/external/wpt/webaudio/the-audio-api/the-audioparam-interface/k-rate-gain.html
[add] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/WebKit/LayoutTests/external/wpt/webaudio/the-audio-api/the-audioparam-interface/k-rate-oscillator.html
[add] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/WebKit/LayoutTests/external/wpt/webaudio/the-audio-api/the-audioparam-interface/k-rate-panner.html
[add] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/WebKit/LayoutTests/external/wpt/webaudio/the-audio-api/the-audioparam-interface/k-rate-stereo-panner.html
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/WebKit/LayoutTests/virtual/stable/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/blink/renderer/modules/webaudio/audio_buffer_source_node.cc
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/blink/renderer/modules/webaudio/audio_listener.cc
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/blink/renderer/modules/webaudio/audio_param.cc
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/blink/renderer/modules/webaudio/audio_param.h
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/blink/renderer/modules/webaudio/audio_param.idl
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/blink/renderer/modules/webaudio/audio_param_descriptor.idl
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/blink/renderer/modules/webaudio/audio_worklet_node.cc
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/blink/renderer/modules/webaudio/biquad_dsp_kernel.cc
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/blink/renderer/modules/webaudio/biquad_filter_node.cc
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/blink/renderer/modules/webaudio/constant_source_node.cc
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/blink/renderer/modules/webaudio/delay_node.cc
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/blink/renderer/modules/webaudio/dynamics_compressor_node.cc
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/blink/renderer/modules/webaudio/gain_node.cc
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/blink/renderer/modules/webaudio/oscillator_node.cc
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/blink/renderer/modules/webaudio/panner_node.cc
[modify] https://crrev.com/59636b605b8e4b382a58a4bd8827a3a06d1df42d/third_party/blink/renderer/modules/webaudio/stereo_panner_node.cc