A system for building glyph runs. In the future the builder will
only live in canvas, but it's internal structures facilitate
interacting with the cache a single glyph at a time. When all
the bulk code is in place, only runs will be passed around.
Passing the builder down the text draw stack is temporary.
Change-Id: I6e3ed184b3f3a58b919377f2d31936e971bd8efa
Reviewed-on: https://skia-review.googlesource.com/132928
Reviewed-by: Herb Derby <herb@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Herb Derby <herb@google.com>
59d997a6e1