Add dummy dart:html library for documentation.

lib/html/doc/interface/BiquadFilterNode.dartdoc

Index: lib/html/doc/interface/BiquadFilterNode.dartdoc
diff --git a/lib/html/doc/interface/BiquadFilterNode.dartdoc b/lib/html/doc/interface/BiquadFilterNode.dartdoc
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+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// WARNING:
+//   This file contains documentation that is merged into the real source.
+//   Do not make code changes here.
+
+/// @domName BiquadFilterNode
+interface BiquadFilterNode extends AudioNode {
+
+  static final int ALLPASS = 7;
+
+  static final int BANDPASS = 2;
+
+  static final int HIGHPASS = 1;
+
+  static final int HIGHSHELF = 4;
+
+  static final int LOWPASS = 0;
+
+  static final int LOWSHELF = 3;
+
+  static final int NOTCH = 6;
+
+  static final int PEAKING = 5;
+
+  /** @domName BiquadFilterNode.Q */
+  final AudioParam Q;
+
+  /** @domName BiquadFilterNode.frequency */
+  final AudioParam frequency;
+
+  /** @domName BiquadFilterNode.gain */
+  final AudioParam gain;
+
+  /** @domName BiquadFilterNode.type */
+  int type;
+
+  /** @domName BiquadFilterNode.getFrequencyResponse */
+  void getFrequencyResponse(Float32Array frequencyHz, Float32Array magResponse, Float32Array phaseResponse);
+}