Introduce text blob processing but don't wire it up

Have all the old code paths start using lists in preparation
for introducing text blobs.

Change-Id: I65cc02ee3da63bc3c9492db78a08b0eee3b1f931
Reviewed-on: https://skia-review.googlesource.com/141081
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Herb Derby <herb@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
8 files changed