Mark SkScalerContext::fRec const

Logically the SkScalerContext::fRec should never change after creation
of the SkScalerContext. This was previously implicit, but make this
explicit.

Change-Id: Ifc0db894fcece57d398322f9cb3e2c0b37f61d09
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/974236
Reviewed-by: Daniel Dilan <danieldilan@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
2 files changed