Record SkCanvas::flush().

We can record multiple frames in an .skp by recording SkCanvas::flush().
This should make SkPictures, SkLiteDL, and .skp files all record flush().

Change-Id: I6cf6e0e4ef993530d9f92fa168a53702ffce7d5e
Reviewed-on: https://skia-review.googlesource.com/34081
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
14 files changed