Bug 1056171 - Account for continuations when generating background clip areas. r=roc

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extra : rebase_source : aa554aa075c5d1286a1f32351abec547c151213f
Bug 1057211 - Use DrawTargetDual for component alpha layers when tiling so that we get correct PushGroupAndCopyBackground behaviour. r=nical

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extra : rebase_source : e304d9947d42317e5eeb38c1d30cc5e149472e11
Bug 1057216 - Make DrawTargetCG hold a reference to DataSourceSurface when we're wrapping their data. r=jrmuizel

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extra : rebase_source : ad610592f69294caedcbca5d61c1644120cbec66
Bug 1050788 - Add test for complex path that is entirely clipped out. r=roc

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extra : rebase_source : 3844baef99a92332b0bc4d1b382596f7aea51f40
Bug 1050788 - Fix a bug where cairo's region clipping code incorrectly handled empty clips. r=jrmuizel

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extra : rebase_source : 653c04da802a5e6598638baaaab05c059b46709d