Fix SkString's move constructor

validate() returned a const reference, which meant that the sk_sp field
initialization was actually calling the copy constructor.

Change-Id: I7f454599a56b51189bc30b2656fd59866ad37203
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/700216
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
3 files changed