use unique_ptr for stream api

Bug: skia:6888
Change-Id: I3459b4913982a7cae1c0061697c82cc65ad9a2d8
Reviewed-on: https://skia-review.googlesource.com/26740
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
16 files changed