Bug 883416 (Part 1) - Revert bug 851416. r=dholbert

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extra : rebase_source : 47dae82941038ff7f79f15aee50194276f617f9b
Bug 883416 (Part 2) - Revert bug 846028. r=dholbert

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extra : rebase_source : be11dfe000188dc97b0daef70135d3a9f2d3a513
Bug 883416 (Part 3) - Coalesce invalidations in RasterImage using a listening flag. r=dholbert

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extra : rebase_source : db6a580cacd0f0556c5e38ba1b4fb9924ecf9dfd
Bug 873591 - Make better errors for execute_script failures, r=mdas
Bug 884459 - Do not check mCurrentTaskMessageQueue's emptiness needlessly; r=ehsan