Clean up filterRes handling on the deferred filters path.

Now that SkResizeImageFilter scales from the device origin (not the
saveLayer() origin, badly) and skia filters automatically adjust the
clip bounds to accommodate filter margins, we can remove a lot of the
ugliness from the deferred filters path: we don't need to force the
clip bounds with SkRegion::kReplace_Op, we don't need to save the old
bounds, and we don't need to offset the scale applied to the CTM (it
should be scaled from origin (0, 0)).

We do need to set the clip region before the saveLayer() to the
primitive bounds, however, so that filters aren't drawn outside it
in both the filterRes and non-filterRes case (e.g.,
svg/filters/feImage-preserveAspectratio.svg was failing due to
FEImage draws straddling the clip rect not being clipped).

Test: run svg/filters layout tests with --enable-deferred-filters.

Review URL: https://codereview.chromium.org/177903004

git-svn-id: svn://svn.chromium.org/blink/trunk@167710 bbb929c8-8fbe-4397-9dbb-9b2b20218538