This is in anticipation of adding Animation::SetTimeline(). Once we set the
timeline out of band, there's a chance that getting it could return null so
this patch makes the WebIDL and method name reflect that.
This patch is a fairly minimal rename of the AnimationPlayer interface. It
leaves a bunch of local variables and helper classes still using the word
"player". These will be addressed in subsequent patches that don't require DOM
peer review.
We define KeyframeEffectReadonly in KeyframeEffect.cpp since Web Animations also
defines KeyframeEffect and when we come to implement that I expect we'll define
it in the same class, maybe even using the same object.
This patch also adds a few missing includes in places where
KeyframeEffectReadonly is used so that we're not just cargo-culting it in.
Most of this is fairly obvious. However, the addition of 'override' to
ElementPropertyTransition::Name() is not strictly necessary. It was simply added
because while making these changes I accidentally dropped the 'virtual' keyword
from the method in the superclass and the compiler didn't complain. Adding this
will hopefully make it harder to create the same bug in the future.
