There are many derived classes is not overriding these methods.
Such as 
AnalyserNode,
AudioBuffferSourceNode.h
ChannelMergerNode.h
ChannelSplitterNode.h
ConstantSourceNode.h
DefaultAudioDestinationNode.h
....
and list continues.

By making these methods as pure virtual methods, we need to add
  double TailTime() const override { return 0; }
  double LatencyTime() const override { return 0; }
in all these classes.. 

rtoy@
Shall I change all these classes ? 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/932d94a4b055c97d2e4a33363d0934340904b4e6

commit 932d94a4b055c97d2e4a33363d0934340904b4e6
Author: Shanmuga Pandi M <shanmuga.m@samsung.com>
Date: Thu Jun 29 11:01:08 2017

Make AudioNode::TailTime() and AudioNode::LatencyTime() as pure virtual.

Making AudioNode::TailTime() and AudioNode::LatencyTime()
as pure virtual methods, so that derived node class
must implement its own version instead of inheriting
a default from AudioNode, which is probably wrong.

Bug:  733370 
Change-Id: I1ccc9388768a1a0e6883d90c619ca13f58c98876
Reviewed-on: https://chromium-review.googlesource.com/549680
Reviewed-by: Raymond Toy <rtoy@chromium.org>
Commit-Queue: Shanmuga Pandi <shanmuga.m@samsung.com>
Cr-Commit-Position: refs/heads/master@{#483320}
[modify] https://crrev.com/932d94a4b055c97d2e4a33363d0934340904b4e6/third_party/WebKit/Source/modules/webaudio/AudioBasicInspectorNode.h
[modify] https://crrev.com/932d94a4b055c97d2e4a33363d0934340904b4e6/third_party/WebKit/Source/modules/webaudio/AudioNode.cpp
[modify] https://crrev.com/932d94a4b055c97d2e4a33363d0934340904b4e6/third_party/WebKit/Source/modules/webaudio/AudioNode.h
[modify] https://crrev.com/932d94a4b055c97d2e4a33363d0934340904b4e6/third_party/WebKit/Source/modules/webaudio/AudioScheduledSourceNode.h
[modify] https://crrev.com/932d94a4b055c97d2e4a33363d0934340904b4e6/third_party/WebKit/Source/modules/webaudio/ChannelMergerNode.h
[modify] https://crrev.com/932d94a4b055c97d2e4a33363d0934340904b4e6/third_party/WebKit/Source/modules/webaudio/ChannelSplitterNode.h
[modify] https://crrev.com/932d94a4b055c97d2e4a33363d0934340904b4e6/third_party/WebKit/Source/modules/webaudio/DefaultAudioDestinationNode.h
[modify] https://crrev.com/932d94a4b055c97d2e4a33363d0934340904b4e6/third_party/WebKit/Source/modules/webaudio/GainNode.h
[modify] https://crrev.com/932d94a4b055c97d2e4a33363d0934340904b4e6/third_party/WebKit/Source/modules/webaudio/MediaElementAudioSourceNode.h
[modify] https://crrev.com/932d94a4b055c97d2e4a33363d0934340904b4e6/third_party/WebKit/Source/modules/webaudio/MediaStreamAudioSourceNode.h
[modify] https://crrev.com/932d94a4b055c97d2e4a33363d0934340904b4e6/third_party/WebKit/Source/modules/webaudio/OfflineAudioDestinationNode.h
[modify] https://crrev.com/932d94a4b055c97d2e4a33363d0934340904b4e6/third_party/WebKit/Source/modules/webaudio/StereoPannerNode.h