Reviewed by Adam Barth.

        [chromium] need DragImage implementation
        https://bugs.webkit.org/show_bug.cgi?id=35811

        Add two files that failed to get added in my previous patch.

        * platform/chromium/DragImageChromiumMac.cpp: Added.
        (WebCore::dragImageSize):
        (WebCore::deleteDragImage):
        (WebCore::scaleDragImage):
        (WebCore::dissolveDragImageToFraction):
        (WebCore::createDragImageFromImage):
        (WebCore::createDragImageIconForCachedImage):
        * platform/chromium/DragImageChromiumSkia.cpp: Added.
        (WebCore::dragImageSize):
        (WebCore::deleteDragImage):
        (WebCore::scaleDragImage):
        (WebCore::dissolveDragImageToFraction):
        (WebCore::createDragImageFromImage):
        (WebCore::createDragImageIconForCachedImage):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@57032 268f45cc-cd09-0410-ab3c-d52691b4dbfc