Fix analysis issues in the video_player plugin Android code (flutter#291)

Author: tvolkert

packages/video_player/android/src/main/java/io/flutter/videoplayer/VideoPlayerPlugin.java

@@ -25,12 +25,11 @@
 import java.util.Map;
 
 public class VideoPlayerPlugin implements MethodCallHandler {
-  private class VideoPlayer {
+  private static class VideoPlayer {
     private final TextureRegistry.SurfaceTextureEntry textureEntry;
     private final MediaPlayer mediaPlayer;
     private EventChannel.EventSink eventSink;
     private final EventChannel eventChannel;
-    private boolean isPlaying = false;
     private boolean isInitialized = false;
 
     @TargetApi(21)