Bug 874295. On non-Android platforms (and eventually for Android), use call GetDefaultScale instead of GetDevicePixelsPerMetaViewportPixel. r=mbrubeck

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extra : rebase_source : 92e6c476f847349969430d96fa363b6f46bb8d5b
Bug 874295. Fix viewport tests. r=mbrubeck

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extra : rebase_source : 48252cd24f804fbac3c6a7eaf7792fbc9c7584b8