Bug 974709 - Use a separate texture for each X11TextureSource and keep the pixmap bound. r=nical

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extra : rebase_source : 06012985e185f517d8a807788e35ea1efcaf39d8
Bug 975592 - Make sure we find the correct composition manager when updating child process layer trees. r=nical

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extra : rebase_source : 5e1457117293c74a362a0570aca2673c90038334