Before this CL, EraseIf was defined in flat_tree.h, but that file can
only be included by the flat_map/flat_set implementation, as it's an
internal file with limited visibility.
This CL will move the flat_tree's base EraseIf implementation to the
internal namespace and define specific variants of it in flat_map.h and
flat_set.h
Bug: webrtc:12689
Change-Id: Idf31915f4abe36ad302c1da669b702974a27c647
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/225206
Commit-Queue: Victor Boivie <boivie@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34431}
5900ba0ee8