Moves readFromMemory, writeToMemory to private section.
No sign that these are called from google3, android,
chromium, but function names are common enough that
it's hard to know for sure.
These are used inside templates internally and for
testing, so it is not quite as simple as adding alternate
entry points in SkMatrixPriv.
R=reed@google.com
Bug: skia:6898
Change-Id: I1fac142f4bf0f38608ea93438c46f39147606c4d
Reviewed-on: https://skia-review.googlesource.com/62361
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Cary Clark <caryclark@google.com>
6d6d603c81