add testing code for serialized Slugs

By setting the compile time flag:
SK_EXPERIMENTAL_SIMULATE_DRAWGLYPHRUNLIST_WITH_SLUG_STRIKE_SERIALIZE
will cause all SkTextBlobs to be rendered by analyzing the Slug
to create strike cache differences and serialize the Blob to a Slug.
Then the serialized strike cache differences are used to populate
the strike cache using a different TypefaceIDs using SkTypeface_Remote
as a proxy for the real SkTypeface. This will create a hard break
between the original glyph data, and the proxied glyph data.
It will then deserialize the Slug doing TypefaceID translation to
the SkTypeface_Remote, and draw the unflattened Slug.

Bug: chromium:1278340

Change-Id: I0f1980dee966b1092a99741793aed9d138451f4d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/510228
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Herb Derby <herb@google.com>
5 files changed