expose MediaProjection

BUG=None

Change-Id: I82f97f02272d882cd2fdc0d9869f2879ba3bbc30
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/182440
Commit-Queue: Bin Zhu <ricebin@google.com>
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31993}

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

@@ -75,6 +75,11 @@ public class ScreenCapturerAndroid implements VideoCapturer, VideoSink {
     }
   }
 
+  @Nullable
+  public MediaProjection getMediaProjection() {
+    return mediaProjection;
+  }
+
   @Override
   // TODO(bugs.webrtc.org/8491): Remove NoSynchronizedMethodCheck suppression.
   @SuppressWarnings("NoSynchronizedMethodCheck")