nsresult
SVGAnimatedTransformList::SetBaseValueString(const nsAString& aValue)
{
  SVGTransformList newBaseValue;
  nsresult rv = newBaseValue.SetValueFromString(aValue);
  if (NS_FAILED(rv)) {
    return rv;
  }

  DOMSVGAnimatedTransformList *domWrapper =
    DOMSVGAnimatedTransformList::GetDOMWrapperIfExists(this);
  if (domWrapper) {
    // We must send this notification *before* changing mBaseVal! If the length
    // of our baseVal is being reduced, our baseVal's DOM wrapper list may have
    // to remove DOM items from itself, and any removed DOM items need to copy
    // their internal counterpart values *before* we change them.
    //
    domWrapper->InternalBaseValListWillChangeLengthTo(newBaseValue.Length());
  }

  // We don't need to call DidChange* here - we're only called by
  // nsSVGElement::ParseAttribute under Element::SetAttr,
  // which takes care of notifying.

  rv = mBaseVal.CopyFrom(newBaseValue);
  if (NS_FAILED(rv) && domWrapper) {
    // Attempting to increase mBaseVal's length failed - reduce domWrapper
    // back to the same length:
    domWrapper->InternalBaseValListWillChangeLengthTo(mBaseVal.Length());
  } else {
    mIsAttrSet = true;
  }
  return rv;
}
void
SVGAnimatedTransformList::ClearBaseValue()
{
  DOMSVGAnimatedTransformList *domWrapper =
    DOMSVGAnimatedTransformList::GetDOMWrapperIfExists(this);
  if (domWrapper) {
    // We must send this notification *before* changing mBaseVal! (See above.)
    domWrapper->InternalBaseValListWillChangeLengthTo(0);
  }
  mBaseVal.Clear();
  mIsAttrSet = false;
  // Caller notifies
}
void
SVGAnimatedTransformList::ClearAnimValue(nsSVGElement *aElement)
{
  DOMSVGAnimatedTransformList *domWrapper =
    DOMSVGAnimatedTransformList::GetDOMWrapperIfExists(this);
  if (domWrapper) {
    // When all animation ends, animVal simply mirrors baseVal, which may have
    // a different number of items to the last active animated value. We must
    // keep the length of our animVal's DOM wrapper list in sync, and again we
    // must do that before touching mAnimVal. See comments above.
    //
    domWrapper->InternalAnimValListWillChangeLengthTo(mBaseVal.Length());
  }
  mAnimVal = nullptr;
  aElement->DidAnimateTransformList();
}
nsresult
SVGAnimatedTransformList::SetAnimValue(const SVGTransformList& aValue,
                                       nsSVGElement *aElement)
{
  DOMSVGAnimatedTransformList *domWrapper =
    DOMSVGAnimatedTransformList::GetDOMWrapperIfExists(this);
  if (domWrapper) {
    // A new animation may totally change the number of items in the animVal
    // list, replacing what was essentially a mirror of the baseVal list, or
    // else replacing and overriding an existing animation. When this happens
    // we must try and keep our animVal's DOM wrapper in sync (see the comment
    // in DOMSVGAnimatedTransformList::InternalBaseValListWillChangeLengthTo).
    //
    // It's not possible for us to reliably distinguish between calls to this
    // method that are setting a new sample for an existing animation, and
    // calls that are setting the first sample of an animation that will
    // override an existing animation. Happily it's cheap to just blindly
    // notify our animVal's DOM wrapper of its internal counterpart's new value
    // each time this method is called, so that's what we do.
    //
    // Note that we must send this notification *before* setting or changing
    // mAnimVal! (See the comment in SetBaseValueString above.)
    //
    domWrapper->InternalAnimValListWillChangeLengthTo(aValue.Length());
  }
  if (!mAnimVal) {
    mAnimVal = new SVGTransformList();
  }
  nsresult rv = mAnimVal->CopyFrom(aValue);
  if (NS_FAILED(rv)) {
    // OOM. We clear the animation, and, importantly, ClearAnimValue() ensures
    // that mAnimVal and its DOM wrapper (if any) will have the same length!
    ClearAnimValue(aElement);
    return rv;
  }
  aElement->DidAnimateTransformList();
  return NS_OK;
}