Move SkWriteBuffer to smart pointers.

The fields fFactorySet and fTFSet and their setting member functions are
changed to use smart pointers instead of manually handling the reference
counting.

Change-Id: I7d8e9f3dff5a7b4770959c5cc143a3ac7289d108
Reviewed-on: https://skia-review.googlesource.com/140348
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
3 files changed