The implicit SkTCopyOnFirstWrite copy-ctor and assignment operator are
incorrect: fObj must point to the local copy, not to the source copy
(when a copy has been made).
Add corrected explicit copy (and move) ctor + assignment operator.
Also add a get() helper to facilitate rawptr access.
Change-Id: Ie3983e12c04eae4f32c40e3e267618cf02008c20
Reviewed-on: https://skia-review.googlesource.com/120442
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
