Fix for <rdar://problem/4616595> REGRESSION: Problems with world 
        clock widget clock hand motion on 9A211 + 4604574

        The second hand on the widget was jiggling because the rotation was 
        messing up the use of the affine transformation matrix while 
        rounding to pixel boundaries in device space. We are mainly 
        concerned with rounding to pixel boundaries with the scale in mind, 
        so this patch extracts the scale to device space from the matrix, 
        and rounds to pixel boundaries using only the scale. This doesn't 
        seem like it is a perfect solution, but it definitely solves the 
        immediate problem. We will probably need to re-address what should 
        happen to avoid pixel cracks with rotations at non-integral scale 
        factors. 

        * platform/cg/GraphicsContextCG.cpp:
        (WebCore::GraphicsContext::roundToDevicePixels):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@15470 268f45cc-cd09-0410-ab3c-d52691b4dbfc