Bug 863498. Get the SurfaceTexture transform every draw. r=nical

ShadowImageLayerOGL::RenderLayer used to call gl()->GetSharedHandleDetails()
directly and uses that result.

This makes us do something similar. As a concequence we also drop the
mTextureTransform member because we are not caching it anymore.

I do wonder if it would make more sense for the content thread to send
the transform along with the update to make sure that it always matches.
This would also make it so that we have no chance of causing a GC
in the compositor to get the transform by calling through java.