NuPlayer: queue a deferred scan sources when flushing during scan

also refactor code to move scheduleRequestBuffers to decoder base.

bug: 20267388
Change-Id: I48f16adc6b4d4008f8fcda8b3b01c595ad199f8b
diff --git a/media/libmediaplayerservice/nuplayer/NuPlayerDecoder.h b/media/libmediaplayerservice/nuplayer/NuPlayerDecoder.h
index 0c0e90c..9f0ef1b5 100644
--- a/media/libmediaplayerservice/nuplayer/NuPlayerDecoder.h
+++ b/media/libmediaplayerservice/nuplayer/NuPlayerDecoder.h
@@ -45,7 +45,7 @@
     virtual void onResume(bool notifyComplete);
     virtual void onFlush();
     virtual void onShutdown(bool notifyComplete);
-    virtual void doRequestBuffers();
+    virtual bool doRequestBuffers();
 
 private:
     enum {