Reinstate "API for periodically regathering ICE candidates"

Use rtc::SystemTimeNanos() instead of std::random_device() for PRNG seed
to avoid crashing when /dev/urandom is unavailable.

This reverts commit 3beb20720db349f651c2c04970c45b1b171c025c.

Bug: webrtc:7969
Change-Id: I5ed58a789939ee4caa99ac3abf9cab18e3e19c69
Reviewed-on: https://chromium-review.googlesource.com/572070
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#19033}
diff --git a/webrtc/api/peerconnectioninterface.h b/webrtc/api/peerconnectioninterface.h
index d6cabf4..6649f2a 100644
--- a/webrtc/api/peerconnectioninterface.h
+++ b/webrtc/api/peerconnectioninterface.h
@@ -453,6 +453,13 @@
     // (STUN pings), in milliseconds.
     rtc::Optional<int> ice_check_min_interval;
 
+
+    // ICE Periodic Regathering
+    // If set, WebRTC will periodically create and propose candidates without
+    // starting a new ICE generation. The regathering happens continuously with
+    // interval specified in milliseconds by the uniform distribution [a, b].
+    rtc::Optional<rtc::IntervalRange> ice_regather_interval_range;
+
     //
     // Don't forget to update operator== if adding something.
     //