The plan is to replace Members() with Attributes() instead.
For backwards-compatability during the transition, Attribute implements
RTCStatsMemberInterface but the two classes serve the same purpose
which is to allow iterating all metrics of a stats object.
The reason for moving away from "members" is that we already have a way
to express a variable that maybe has a value: absl::optional<T>. The
only information the member adds is the const char* name(), which we'll
move to Attribute in a future CL.
We don't need to maintain an RTCStatsMemberInterface::Type enum in the
future because absl::variant<T> has absl::holds_alternative<T>.
Step 1: Add Attributes().
Step 2: Migrate to Attributes() and delete Members().
Step 3: Replaces all uses of RTCStatsMember<T> with absl::optional<T>
and delete RTCStatsMember + RTCStatsMemberInterface.
Bug: webrtc:15164
Change-Id: I3fdd5b24214bb5cc340a54a0171df73b516e1803
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/333840
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#41507}
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