Bug 868082. Allow SetIsFixedPosition to be used on layers with transforms. In CompositorParent, use the animated transform value as the base transform in CompositorParent::TransformFixedLayers when it has been set by the animation sampler. r=cwiis

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extra : rebase_source : 3b809428bf8740753a98defc30ad7b7d96339442
Bug 857538 - Diagnostic for HWNDGetter leak. r=ted