add client-context to SkWriteBuffer

Bug: skia:
Change-Id: I56c36060442c4008b09f322fb1d19e81cd75f910
Reviewed-on: https://skia-review.googlesource.com/66860
Reviewed-by: Khusal Sagar <khushalsagar@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed