Merge mozilla-central to mozilla-inbound

--HG--
rename : browser/themes/osx/tabbrowser/connecting@2x.png => browser/themes/windows/tabbrowser/connecting@2x.png
rename : browser/themes/osx/tabbrowser/loading@2x.png => browser/themes/windows/tabbrowser/loading@2x.png
rename : browser/themes/windows/tabbrowser/tab-background-end.png => browser/themes/windows/tabbrowser/tab-background-end-preWin10.png
rename : browser/themes/windows/tabbrowser/tab-background-end@2x.png => browser/themes/windows/tabbrowser/tab-background-end-preWin10@2x.png
rename : browser/themes/windows/tabbrowser/tab-background-middle.png => browser/themes/windows/tabbrowser/tab-background-middle-preWin10.png
rename : browser/themes/windows/tabbrowser/tab-background-middle@2x.png => browser/themes/windows/tabbrowser/tab-background-middle-preWin10@2x.png
rename : browser/themes/windows/tabbrowser/tab-background-start.png => browser/themes/windows/tabbrowser/tab-background-start-preWin10.png
rename : browser/themes/windows/tabbrowser/tab-background-start@2x.png => browser/themes/windows/tabbrowser/tab-background-start-preWin10@2x.png
extra : rebase_source : f873d375eae8f1ee22151e5891b4fc3cc576d599