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/NuPlayerDecoderBase.h b/media/libmediaplayerservice/nuplayer/NuPlayerDecoderBase.h
index 97e9269..e09fe04 100644
--- a/media/libmediaplayerservice/nuplayer/NuPlayerDecoderBase.h
+++ b/media/libmediaplayerservice/nuplayer/NuPlayerDecoderBase.h
@@ -69,8 +69,7 @@
     virtual void onShutdown(bool notifyComplete) = 0;
 
     void onRequestInputBuffers();
-    void scheduleRequestBuffers();
-    virtual void doRequestBuffers() = 0;
+    virtual bool doRequestBuffers() = 0;
     virtual void handleError(int32_t err);
 
     sp<AMessage> mNotify;