Use floats for SkPicture sizing.

Minor cleanup: Skia now takes SkScalar picture width/height args,
so we can pass our float size directly.

R=schenney@chromium.org,senorblanco@chromium.org

Review URL: https://codereview.chromium.org/679853002

git-svn-id: svn://svn.chromium.org/blink/trunk@184406 bbb929c8-8fbe-4397-9dbb-9b2b20218538