Move /webrtc/api/android files to /webrtc/sdk/android

I decided to make one webrtc/sdk/android/BUILD.gn for both tests and Java/jni src.

External dependencies needs to be updated after this CL.

Future work is required to clean up the Android api and move
implementation details to /webrtc/sdk/android/src.

BUG=webrtc:5882,webrtc:6804
NOPRESUBMIT=True

Review-Url: https://codereview.webrtc.org/2547483003
Cr-Commit-Position: refs/heads/master@{#15443}

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

@@ -0,0 +1,59 @@
+/*
+ *  Copyright 2015 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+package org.webrtc;
+
+/** Java wrapper for a C++ RtpReceiverInterface. */
+public class RtpReceiver {
+  final long nativeRtpReceiver;
+
+  private MediaStreamTrack cachedTrack;
+
+  public RtpReceiver(long nativeRtpReceiver) {
+    this.nativeRtpReceiver = nativeRtpReceiver;
+    long track = nativeGetTrack(nativeRtpReceiver);
+    // We can assume that an RtpReceiver always has an associated track.
+    cachedTrack = new MediaStreamTrack(track);
+  }
+
+  public MediaStreamTrack track() {
+    return cachedTrack;
+  }
+
+  public boolean setParameters(RtpParameters parameters) {
+    return nativeSetParameters(nativeRtpReceiver, parameters);
+  }
+
+  public RtpParameters getParameters() {
+    return nativeGetParameters(nativeRtpReceiver);
+  }
+
+  public String id() {
+    return nativeId(nativeRtpReceiver);
+  }
+
+  public void dispose() {
+    cachedTrack.dispose();
+    free(nativeRtpReceiver);
+  }
+
+  // This should increment the reference count of the track.
+  // Will be released in dispose().
+  private static native long nativeGetTrack(long nativeRtpReceiver);
+
+  private static native boolean nativeSetParameters(
+      long nativeRtpReceiver, RtpParameters parameters);
+
+  private static native RtpParameters nativeGetParameters(long nativeRtpReceiver);
+
+  private static native String nativeId(long nativeRtpReceiver);
+
+  private static native void free(long nativeRtpReceiver);
+};