Bug 824217 - Remove some easy-to-remove tests of JSRESOLVE_ASSIGNING.  r=bz

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extra : rebase_source : 2605d559d48b9ccd985bd860f13ab7b1b53ab048
Bug 825692. Avoid layerizing scrollframes that don't have scrollbar boxes. r=roc

Input boxes have overflow:auto but don't have scrollbar boxes. This prevents
us from layerizing them.

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extra : rebase_source : 24d305a019f67ea2d2529bd25815209bff4485c7