Remove uniqueID from all filter serialization.

(This is essentially a revert of https://codereview.chromium.org/503833002/.)

This was necessary back when SkPaint was flattened even for in-process use. Now that we only flatten SkPaint for cross-process use, there's no need to serialize UniqueIDs.

Note: SkDropShadowImageFilter is being constructed with a croprect and UniqueID (of 0) in Blink. I've made the uniqueID param default to 0 temporarily, until this rolls in and Blink can be changed. (Blink can't be changed first, since unlike the other filters, there's no constructor that takes a cropRect but not a uniqueID.)

BUG=skia:

Review URL: https://codereview.chromium.org/1019493002
37 files changed