Factor out growAndPushBack into a helper function.

This uses a universal reference and std::forward to enable some
code sharing. Let's see if it affects code size.

Bug: b/40044928
Change-Id: I172f9a3ea60308fa2e7301c078487f33af703071
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/766597
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Herb Derby <herb@google.com>
1 file changed