Add glyph cache warming - prototype

A system for prewarming the cache using a single "RPC"
This improve performance by ~5X.

This is a checkin of rough code so I can use small
changes clean it up.

BUG=skia:7515

Change-Id: Id0192b4f533c257b0a7eea0170b1e25c336d6432
Reviewed-on: https://skia-review.googlesource.com/105440
Reviewed-by: Herb Derby <herb@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
5 files changed