Modify IceControllerInterface::SelectConnectionToPing - step 3

this is a NOP refactoring, that modify return type
of IceControllerInterface::SelectConnectionToPing to a struct
(rather than existing pair). The modification is done
so that one can safely add new return values in the struct.

Step 1) Create a typedef for return value.
- merge downstream and change it to start using new type.
Step 2) Change typedef to struct,
adding constructors from old type to new type
merge and change downstream to use "real" constructors
Step 3) remove temporary constructors
Step 4) Eat cake

Each step requires a merge downstream, with corresponding
changes there.

Bug: chromium:1024965
Change-Id: I46ad4a58426a7d33b84bc78caab55893315d25c1
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/171874
Commit-Queue: Jonas Oreland <jonaso@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30921}

p2p/base/ice_controller_interface.h

@@ -78,15 +78,16 @@ class IceControllerInterface {
     PingResult(const Connection* conn, int _recheck_delay_ms)
         : connection(conn), recheck_delay_ms(_recheck_delay_ms) {}
 
-    // A temporary constructor while merging.
-    // Will be removed once downstream has been updated.
-    PingResult(const std::pair<Connection*, int>& pair)  // NOLINT
-        : connection(pair.first), recheck_delay_ms(pair.second) {}
-
     // Connection that we should (optionally) ping.
     const absl::optional<const Connection*> connection;
 
-    // The delay before calling SelectConnectionToPing() again.
+    // The delay before P2PTransportChannel shall call SelectConnectionToPing()
+    // again.
+    //
+    // Since the IceController determines which connection to ping and
+    // only returns one connection at a time, the recheck_delay_ms does not have
+    // any obvious implication on bitrate for pings. E.g the recheck_delay_ms
+    // will be shorter if there are more connections available.
     const int recheck_delay_ms = 0;
   };