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This adds serialization/deserialization/testing for most of the
internals of PaintFlags.  SkValidatingSerializeFlattenable is used for
more complex Skia objects.

Still remaining to be handled are PaintShader and SkTypeface.
Additionally, SkValidatingSerializeFlattenable ignores
SkPictureImageFilters for security purposes and so these will have to be
handled in some other manner in the future.

This serialization is not yet called while running Chrome yet.  This is
all for testing purposes at this point.

Bug: 737629
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ic1787721e7518367dca0c40f7a6a438bca980701
Reviewed-on: https://chromium-review.googlesource.com/578321Reviewed-by: Vladimir Levin <vmpstr@chromium.org>
Commit-Queue: enne <enne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488678}