CSSLengthInterpolationType::apply contains an "#if ENABLE(ASSERT)" clause that references AnimatableValue.
alancutter:
"""
The comment for it is wrong however, it's not comparing this code path with AnimatedStyleBuilder's, instead it's comparing the fast path with the slow path just below. It's not necessary to use AnimatableValues here either, it colud use LengthPropertyFunctions::getLength() instead.
"""
This is a minor code health issue but is technically blocking the complete removal of AnimatableValue ( issue 442163 ).
Comment 1 by alancutter@chromium.org
, Jul 22 2016