Release camera statistics after switching camera on CameraCapturer.

BUG=webrtc:6397
TBR=magjed@webrtc.org
NOTRY=True

Review-Url: https://codereview.webrtc.org/2353263002
Cr-Commit-Position: refs/heads/master@{#14323}

webrtc/api/android/java/src/org/webrtc/CameraCapturer.java

@@ -396,6 +396,8 @@ public abstract class CameraCapturer implements CameraVideoCapturer {
       }
 
       Logging.d(TAG, "switchCamera: Stopping session");
+      cameraStatistics.release();
+      cameraStatistics = null;
       currentSession.stop();
       currentSession = null;