Auto merge of #21750 - Manishearth:biquad, r=ferjm

Implement BiquadFilterNode

A bunch of tests still fail but some of it may be a timing issue, looking at it the tests are *at least* affected by https://github.com/servo/servo/issues/21659 (changing how they work to avoid problems from that does not make them pass but does change the exact value of the error), so I feel like I should fix that first before investigating these.

r? @ferjm

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components/script/dom/webidls/BaseAudioContext.webidl

@@ -38,7 +38,7 @@ interface BaseAudioContext : EventTarget {
   [Throws] AnalyserNode createAnalyser();
   [Throws]  GainNode createGain();
   // DelayNode createDelay(optional double maxDelayTime = 1);
-  // BiquadFilterNode createBiquadFilter();
+  [Throws] BiquadFilterNode createBiquadFilter();
   // IIRFilterNode createIIRFilter(sequence<double> feedforward,
   //                               sequence<double> feedback);
   // WaveShaperNode createWaveShaper();

components/script/dom/webidls/BiquadFilterNode.webidl

@@ -0,0 +1,39 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+/*
+ * The origin of this IDL file is
+ * https://webaudio.github.io/web-audio-api/#biquadfilternode
+ */
+
+enum BiquadFilterType {
+  "lowpass",
+  "highpass",
+  "bandpass",
+  "lowshelf",
+  "highshelf",
+  "peaking",
+  "notch",
+  "allpass"
+};
+
+dictionary BiquadFilterOptions : AudioNodeOptions {
+  BiquadFilterType type = "lowpass";
+  float Q = 1;
+  float detune = 0;
+  float frequency = 350;
+  float gain = 0;
+};
+
+[Exposed=Window,
+ Constructor (BaseAudioContext context, optional BiquadFilterOptions options)]
+interface BiquadFilterNode : AudioNode {
+  attribute BiquadFilterType type;
+  readonly attribute AudioParam frequency;
+  readonly attribute AudioParam detune;
+  readonly attribute AudioParam Q;
+  readonly attribute AudioParam gain;
+  // the AudioParam model of https://github.com/servo/servo/issues/21659 needs to
+  // be implemented before we implement this
+  // void getFrequencyResponse (Float32Array frequencyHz, Float32Array magResponse, Float32Array phaseResponse);
+};