Disable the automatic pixel doubling in canvas backing stores on high dpi devices. This will potentially make canvases look worse of high dpi displays, but only if they were ignoring devicePixelRatio. Since the majority of high dpi displays *do not* auto-double (including mobile devices and other desktop browsers), this provides consistency and less chance of unnecessary memory use.
Created attachment 199911 [details]
Committed r149261: <http://trac.webkit.org/changeset/149261>