Change getMetrics to the final API prepareForDrawing

Change the name, and add the atlas limit parameter.

Change-Id: Ic718d06d483667d7a341b74c280bc3fd016289ff
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/207314
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
7 files changed