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We need a version-skew stable mojo transport for UI images. The skia
bitmap serializers have been stable for some time, so tidy them up
and mark them as [Stable].

* Transport color spaces explicitly as a 7-float transfer function
  and 9-float transform matrix to XYZ D50. SkColorSpace::serialize()
  depends on the layout of internal Skia structs that might change.
* Rename ColorType INDEX_8 as DEPRECATED, since it doesn't exist any
  more in skia.
* Don't try to deserialize images with unreasonably large height/width
  (addresses a TODO)
* CHECK-fail before sending a bitmap with negative height/width, rather
  than sending an empty one
* Mark skia mojoms as [Stable]
* Mark mojo_base.mojom.BigBuffer as [Stable], since it's a dependency

See go/lacros-image-transport for background.

Bug: 1116652
Test: skia_unittests
Change-Id: I229cc405901a607ae613c410d7df5b92f03caf54
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2368484Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Greg Kerr <kerrnel@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803234}