Revert "Remove all notion of transport from the API."

This reverts commit 4961a938586e3c46cf80f15ecb70a011324bfe59.

Reason for revert: Breaks MSVC

Original change's description:
> Remove all notion of transport from the API.
> 
> There is only a need to pass buffers in and out of the system.
> All transport is external to the system.
> 
> Change-Id: I26dfc8e0b4cce9969395c96d5230078e7dca3f3d
> Reviewed-on: https://skia-review.googlesource.com/119062
> Commit-Queue: Herb Derby <herb@google.com>
> Reviewed-by: Khushal Sagar <khushalsagar@google.com>

TBR=herb@google.com,reed@google.com,khushalsagar@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I62cbac1be4483702ba7464822d93fb9f818f88b7
Reviewed-on: https://skia-review.googlesource.com/119580
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Herb Derby <herb@google.com>
3 files changed