More SaveFlags removal twiddling.

This is a follow up to https://codereview.chromium.org/338913002/. More
tweaks to allow migrating clients to the new API.

1) switch the shim call direction willSave(SaveFlags) -> willSave()
   (internal users are still using the former, so external overriders of
    the latter will not be notified otherwise - doh)
2) ensure willSave() stays visible in SkProxyCanvas (Chromium's
   TimingCanvas attempts to call it explicitly).

BUG=skia:2297
R=reed@google.com

Author: fmalita@chromium.org

Review URL: https://codereview.chromium.org/334393008
2 files changed