move SkWriteBuffer.h to src

Need this to land first: https://chromium-review.googlesource.com/c/chromium/src/+/834714

Bug: skia:
Change-Id: I426bc3d9b5c4382b5b874b991e37fdd1725bd9a3
Reviewed-on: https://skia-review.googlesource.com/87301
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed