Now, remove Layer::mSourceURI, there are several benefit of doing this:
1. Reduce the size of nsStyleImage::Layer.
2. By storing style image and url information in nsStyleImage, we can remove
many verbose comments. That is becasue there is no need to explain why we use
mSourceURI here, or why we use nsStyleImage there anymore.
3. Since all inforamtion is stored in on place, nsStyleImage, we can setup image
request or URLs by one single Gecko_SetUrlImageValue call.
MozReview-Commit-ID: 7aTQobddTB1
--HG--
extra : rebase_source : 247e3b66c727a9116c58d3d6ff3ae0f7a58f2338
21a1b43445