Make sure we mark Plots in use for all regenerate cases

Bug: b/118850208
Change-Id: I6c0b6d8cb8831baefbe1dc9eebe7fef337a467e6
Reviewed-on: https://skia-review.googlesource.com/c/174590
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
4 files changed