Coalesce proxy object freeing in do_free_pages.
Coalesce proxy object freeing in do_free_pages.

We can only have a non-nullptr proxy object if the span was sampled.  This
logic was previously separated due to some parts holding the pageheap_lock
while other parts did not, but now this code runs entirely without the lock.

PiperOrigin-RevId: 471416342
Change-Id: I2661046bed77081f16b552dd9bed0d54e6ff08b4

google/tcmalloc,google/tcmalloc,google/tcmalloc