Return the `T*` pointer back to the caller in SymbolTable::add.

This makes the add() interface more closely aligned with
takeOwnershipOfXxxxx().

Change-Id: Iafd116fa86bd8ccfe07b730ebcd74d5304967878
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/310069
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
5 files changed