Add Stable Writable Connection Ping Interval parameter to RTCConfiguration.

Bug: webrtc:12642
Change-Id: I543760d49f87130d717c7cf0eca7d2d2f45e8eac
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/215242
Reviewed-by: Jonas Oreland <jonaso@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Derek Bailey <derekbailey@google.com>
Cr-Commit-Position: refs/heads/master@{#33751}

sdk/android/api/org/webrtc/PeerConnection.java

@@ -501,6 +501,9 @@ public class PeerConnection {
     // to keep NAT bindings open.
     // The default value in the implementation is used if this field is null.
     @Nullable public Integer stunCandidateKeepaliveIntervalMs;
+    // The interval in milliseconds of pings sent when the connection is stable and writable.
+    // The default value in the implementation is used if this field is null.
+    @Nullable public Integer stableWritableConnectionPingIntervalMs;
     public boolean disableIPv6OnWifi;
     // By default, PeerConnection will use a limited number of IPv6 network
     // interfaces, in order to avoid too many ICE candidate pairs being created
@@ -589,6 +592,7 @@ public class PeerConnection {
       iceUnwritableTimeMs = null;
       iceUnwritableMinChecks = null;
       stunCandidateKeepaliveIntervalMs = null;
+      stableWritableConnectionPingIntervalMs = null;
       disableIPv6OnWifi = false;
       maxIPv6Networks = 5;
       disableIpv6 = false;
@@ -735,6 +739,12 @@ public class PeerConnection {
       return stunCandidateKeepaliveIntervalMs;
     }
 
+    @Nullable
+    @CalledByNative("RTCConfiguration")
+    Integer getStableWritableConnectionPingIntervalMs() {
+      return stableWritableConnectionPingIntervalMs;
+    }
+
     @CalledByNative("RTCConfiguration")
     boolean getDisableIPv6OnWifi() {
       return disableIPv6OnWifi;