Not a dupe, but just linking to related bug: TypeErrors for invalid easings  crbug.com/601672 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f760e7025c61bd64c3a6bdcf22b1af294ebcad90

commit f760e7025c61bd64c3a6bdcf22b1af294ebcad90
Author: alancutter <alancutter@chromium.org>
Date: Wed Apr 27 10:25:08 2016

Web Animations: Throw TypeErrors for invalid timing parameters

This change throws TypeErrors when invalid parameters are given
for the following AnimationEffectTiming parameters:
 - iterationStart
 - iterations
 - duration

See spec for valid inputs:
https://w3c.github.io/web-animations/#animationeffecttiming

BUG= 605450 

Review URL: https://codereview.chromium.org/1906463002

Cr-Commit-Position: refs/heads/master@{#390040}

[modify] https://crrev.com/f760e7025c61bd64c3a6bdcf22b1af294ebcad90/third_party/WebKit/LayoutTests/imported/web-platform-tests/web-animations/animation-effect-timing/duration-expected.txt
[modify] https://crrev.com/f760e7025c61bd64c3a6bdcf22b1af294ebcad90/third_party/WebKit/LayoutTests/imported/web-platform-tests/web-animations/animation-effect-timing/iterationStart-expected.txt
[modify] https://crrev.com/f760e7025c61bd64c3a6bdcf22b1af294ebcad90/third_party/WebKit/LayoutTests/imported/web-platform-tests/web-animations/animation-effect-timing/iterations-expected.txt
[modify] https://crrev.com/f760e7025c61bd64c3a6bdcf22b1af294ebcad90/third_party/WebKit/LayoutTests/web-animations-api/timed-item-specified-setters.html
[modify] https://crrev.com/f760e7025c61bd64c3a6bdcf22b1af294ebcad90/third_party/WebKit/Source/core/animation/AnimationEffectTiming.cpp
[modify] https://crrev.com/f760e7025c61bd64c3a6bdcf22b1af294ebcad90/third_party/WebKit/Source/core/animation/AnimationEffectTiming.h
[modify] https://crrev.com/f760e7025c61bd64c3a6bdcf22b1af294ebcad90/third_party/WebKit/Source/core/animation/AnimationEffectTiming.idl
[modify] https://crrev.com/f760e7025c61bd64c3a6bdcf22b1af294ebcad90/third_party/WebKit/Source/core/animation/ElementAnimation.h
[modify] https://crrev.com/f760e7025c61bd64c3a6bdcf22b1af294ebcad90/third_party/WebKit/Source/core/animation/KeyframeEffect.cpp
[modify] https://crrev.com/f760e7025c61bd64c3a6bdcf22b1af294ebcad90/third_party/WebKit/Source/core/animation/KeyframeEffectTest.cpp
[modify] https://crrev.com/f760e7025c61bd64c3a6bdcf22b1af294ebcad90/third_party/WebKit/Source/core/animation/Timing.h
[modify] https://crrev.com/f760e7025c61bd64c3a6bdcf22b1af294ebcad90/third_party/WebKit/Source/core/animation/TimingInput.cpp
[modify] https://crrev.com/f760e7025c61bd64c3a6bdcf22b1af294ebcad90/third_party/WebKit/Source/core/animation/TimingInput.h
[modify] https://crrev.com/f760e7025c61bd64c3a6bdcf22b1af294ebcad90/third_party/WebKit/Source/core/animation/TimingInputTest.cpp
[modify] https://crrev.com/f760e7025c61bd64c3a6bdcf22b1af294ebcad90/third_party/WebKit/Source/core/html/HTMLMarqueeElement.js
[modify] https://crrev.com/f760e7025c61bd64c3a6bdcf22b1af294ebcad90/third_party/WebKit/Source/core/inspector/InspectorAnimationAgent.cpp
[modify] https://crrev.com/f760e7025c61bd64c3a6bdcf22b1af294ebcad90/third_party/WebKit/Source/core/style/DataEquivalency.h