Reland "Implement transceiver.stop()"

This is a reland of 11dc6571cb4ff3e71dee1557dfff8d9076e108d3

One fix that makes Web Platform Tests pass in debug mode is applied.

Original change's description:
> Implement transceiver.stop()
>
> This adds RtpTransceiver.StopStandard(), which behaves according to
> the specification at
> https://w3c.github.io/webrtc-pc/#dom-rtcrtptransceiver-stop
>
> It modifies RTCPeerConnection.getTransceivers() to return only
> transceivers that have not been stopped.
>
> Rebase of armax' https://webrtc-review.googlesource.com/c/src/+/172762
>
> Bug: chromium:980879
> Change-Id: I7d383ee874ccc0a006fdcf280496b5d4235425ce
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/180580
> Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
> Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
> Reviewed-by: Guido Urdaneta <guidou@webrtc.org>
> Commit-Queue: Harald Alvestrand <hta@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#31893}

Bug: chromium:980879
Change-Id: Ide31d929ac5ea118d83fdf6a35a592af23f7dfa7
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/181263
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Guido Urdaneta <guidou@webrtc.org>
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31907}
diff --git a/sdk/android/api/org/webrtc/RtpTransceiver.java b/sdk/android/api/org/webrtc/RtpTransceiver.java
index 64d8eb4..021cc90 100644
--- a/sdk/android/api/org/webrtc/RtpTransceiver.java
+++ b/sdk/android/api/org/webrtc/RtpTransceiver.java
@@ -206,13 +206,34 @@
   }
 
   /**
-   * The Stop method irreversibly stops the RtpTransceiver. The sender of this
-   * transceiver will no longer send, the receiver will no longer receive.
-   * https://w3c.github.io/webrtc-pc/#dom-rtcrtptransceiver-stop
+   * The Stop method will for the time being call the StopInternal method.
+   * After a migration procedure, stop() will be equivalent to StopStandard.
    */
   public void stop() {
     checkRtpTransceiverExists();
-    nativeStop(nativeRtpTransceiver);
+    nativeStopInternal(nativeRtpTransceiver);
+  }
+
+  /**
+   * The StopInternal method stops the RtpTransceiver, like Stop, but goes
+   * immediately to Stopped state.
+   */
+  public void stopInternal() {
+    checkRtpTransceiverExists();
+    nativeStopInternal(nativeRtpTransceiver);
+  }
+
+  /**
+   * The StopStandard method irreversibly stops the RtpTransceiver. The sender
+   * of this transceiver will no longer send, the receiver will no longer
+   * receive.
+   *
+   * <p>The transceiver will enter Stopping state and signal NegotiationNeeded.
+   * https://w3c.github.io/webrtc-pc/#dom-rtcrtptransceiver-stop
+   */
+  public void stopStandard() {
+    checkRtpTransceiverExists();
+    nativeStopStandard(nativeRtpTransceiver);
   }
 
   @CalledByNative
@@ -237,7 +258,8 @@
   private static native boolean nativeStopped(long rtpTransceiver);
   private static native RtpTransceiverDirection nativeDirection(long rtpTransceiver);
   private static native RtpTransceiverDirection nativeCurrentDirection(long rtpTransceiver);
-  private static native void nativeStop(long rtpTransceiver);
+  private static native void nativeStopInternal(long rtpTransceiver);
+  private static native void nativeStopStandard(long rtpTransceiver);
   private static native void nativeSetDirection(
       long rtpTransceiver, RtpTransceiverDirection rtpTransceiverDirection);
 }