Bug 931432. Rename nsGfxScrollFrameInner to mozilla::ScrollFrameHelper, and mInner fields to mHelper. r=mats

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extra : rebase_source : 14410be7a6c41a85489f8a802c88a309ddd0fe60
Bug 745485. Optimize positioning offset changes whenever the computed size does not change. r=dholbert

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extra : rebase_source : 16388d3cb0c6ee9acc1416ca0d27b2a53b0062ee
Bug 876321. Track restyling of top/left/right/bottom and treat such nodes as active scrolled roots. r=mattwoodrow

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extra : rebase_source : f92bcf0b60cadefa0197cdffcd6dd9b4eaa6b2d5
Bug 913444. Track restyling of margins and treat such nodes as active scrolled roots. r=mattwoodrow
Restyling margin-top and margin-bottom will typically require reflow and cause
sibling elements to be moved and invalidated, so it's not a big win to layerize
such nodes. However, layerizing them should be relatively harmless.

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extra : rebase_source : b41764dd8ab3651afeec2756c436e059f25b7d46