Switch to the new SkCanvas::willSave() API.

Skia's save() SaveFlags bits are going the way of the dodo. At this
point all callers have been updated to always pass kMatrixClip, but
SkCanvas subclasses also need to use the new willSave() API.

(depends on https://codereview.chromium.org/338833003/ rolling)

BUG=skia:2297
R=reed@google.com,senorblanco@chromium.org,malch@chromium.org

Review URL: https://codereview.chromium.org/338863002

git-svn-id: svn://svn.chromium.org/blink/trunk@176465 bbb929c8-8fbe-4397-9dbb-9b2b20218538