Backout 1a99d532ccd6:ac7fc104c829 (bug 812813) due to bc test failure

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rename : browser/themes/gnomestripe/downloads/download-notification-start.png => browser/themes/gnomestripe/downloads/download-notification.png
rename : browser/themes/pinstripe/downloads/download-notification-start.png => browser/themes/pinstripe/downloads/download-notification.png
rename : browser/themes/winstripe/downloads/download-notification-start.png => browser/themes/winstripe/downloads/download-notification.png
Bug 819252 WheelEvent along x-axis with a modifier key on Mac shouldn't cause zoom action for not preventing following horizontal swip event which will cause going back/forward in the history r=smaug+smichaud
Bug 820538: Added media-ptr check because of NS_DISPATCH_SYNC. r=rjesup