Refactor the vp9_get_frame code for frame parallel.
Refactor the vp9_get_frame code for frame parallel.

In frame parallel decoding mode,  there will be still several frames inside
the decoder when application stop calling vpx_codec_decode to decode frames.
The application will need to keep calling vpx_codec_get_frame to get all the
remaining decoded frames in the decoder.

Change-Id: I2ce8260a91282f045bb9a6093ff8a606b1990f14

pcwalton/libvpx,abwiz0086/webm.libvpx,matanbs/webm.libvpx,ittiamvpx/libvpx,ittiamvpx/libvpx,shacklettbp/aom,matanbs/vp982,mwgoldsmith/libvpx,charup/https---github.com-webmproject-libvpx-,Topopiccione/libvpx,ittiamvpx/libvpx,VTCSecureLLC/libvpx,VTCSecureLLC/libvpx,zofuthan/libvpx,thdav/aom,goodleixiao/vpx,webmproject/libvpx,Topopiccione/libvpx,charup/https---github.com-webmproject-libvpx-,jdm/libvpx,matanbs/webm.libvpx,mwgoldsmith/libvpx,altogother/webm.libvpx,Suvarna1488/webm.libvpx,shacklettbp/aom,shyamalschandra/libvpx,abwiz0086/webm.libvpx,Suvarna1488/webm.libvpx,jdm/libvpx,mwgoldsmith/libvpx,luctrudeau/aom,Distrotech/libvpx,goodleixiao/vpx,jdm/libvpx,charup/https---github.com-webmproject-libvpx-,jacklicn/webm.libvpx,Acidburn0zzz/webm.libvpx,jdm/libvpx,zofuthan/libvpx,jmvalin/aom,goodleixiao/vpx,kalli123/webm.libvpx,hsueceumd/test_hui,Maria1099/webm.libvpx,mbebenita/aom,VTCSecureLLC/libvpx,liqianggao/libvpx,goodleixiao/vpx,ShiftMediaProject/libvpx,openpeer/libvpx_new,mbebenita/aom,goodleixiao/vpx,hsueceumd/test_hui,kleopatra999/webm.libvpx,running770/libvpx,GrokImageCompression/aom,thdav/aom,webmproject/libvpx,shareefalis/libvpx,stewnorriss/libvpx,running770/libvpx,Maria1099/webm.libvpx,felipebetancur/libvpx,gshORTON/webm.libvpx,felipebetancur/libvpx,kalli123/webm.libvpx,smarter/aom,ittiamvpx/libvpx-1,mbebenita/aom,ittiamvpx/libvpx,reimaginemedia/webm.libvpx,running770/libvpx,ittiamvpx/libvpx-1,openpeer/libvpx_new,shyamalschandra/libvpx,kalli123/webm.libvpx,mwgoldsmith/vpx,abwiz0086/webm.libvpx,smarter/aom,abwiz0086/webm.libvpx,shacklettbp/aom,Suvarna1488/webm.libvpx,openpeer/libvpx_new,matanbs/webm.libvpx,shareefalis/libvpx,Suvarna1488/webm.libvpx,kleopatra999/webm.libvpx,n4t/libvpx,openpeer/libvpx_new,jacklicn/webm.libvpx,matanbs/vp982,matanbs/vp982,webmproject/libvpx,iniwf/webm.libvpx,shareefalis/libvpx,shareefalis/libvpx,shyamalschandra/libvpx,gshORTON/webm.libvpx,VTCSecureLLC/libvpx,gshORTON/webm.libvpx,lyx2014/libvpx_c,jmvalin/aom,n4t/libvpx,mbebenita/aom,shacklettbp/aom,iniwf/webm.libvpx,felipebetancur/libvpx,ittiamvpx/libvpx,lyx2014/libvpx_c,iniwf/webm.libvpx,pcwalton/libvpx,jmvalin/aom,kim42083/webm.libvpx,n4t/libvpx,matanbs/vp982,altogother/webm.libvpx,liqianggao/libvpx,mbebenita/aom,lyx2014/libvpx_c,jmvalin/aom,luctrudeau/aom,Acidburn0zzz/webm.libvpx,mwgoldsmith/vpx,iniwf/webm.libvpx,reimaginemedia/webm.libvpx,liqianggao/libvpx,luctrudeau/aom,openpeer/libvpx_new,mwgoldsmith/vpx,goodleixiao/vpx,abwiz0086/webm.libvpx,zofuthan/libvpx,VTCSecureLLC/libvpx,Acidburn0zzz/webm.libvpx,abwiz0086/webm.libvpx,Distrotech/libvpx,altogother/webm.libvpx,ittiamvpx/libvpx-1,thdav/aom,altogother/webm.libvpx,reimaginemedia/webm.libvpx,kim42083/webm.libvpx,matanbs/webm.libvpx,smarter/aom,matanbs/webm.libvpx,Topopiccione/libvpx,running770/libvpx,altogother/webm.libvpx,smarter/aom,Laknot/libvpx,jacklicn/webm.libvpx,smarter/aom,mbebenita/aom,shareefalis/libvpx,n4t/libvpx,kim42083/webm.libvpx,jacklicn/webm.libvpx,ittiamvpx/libvpx,kleopatra999/webm.libvpx,stewnorriss/libvpx,Distrotech/libvpx,thdav/aom,zofuthan/libvpx,ShiftMediaProject/libvpx,GrokImageCompression/aom,zofuthan/libvpx,charup/https---github.com-webmproject-libvpx-,Laknot/libvpx,Distrotech/libvpx,shyamalschandra/libvpx,luctrudeau/aom,gshORTON/webm.libvpx,felipebetancur/libvpx,iniwf/webm.libvpx,Acidburn0zzz/webm.libvpx,stewnorriss/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,ShiftMediaProject/libvpx,Laknot/libvpx,pcwalton/libvpx,kleopatra999/webm.libvpx,mbebenita/aom,jacklicn/webm.libvpx,Distrotech/libvpx,Maria1099/webm.libvpx,luctrudeau/aom,luctrudeau/aom,kim42083/webm.libvpx,pcwalton/libvpx,jmvalin/aom,reimaginemedia/webm.libvpx,hsueceumd/test_hui,mwgoldsmith/libvpx,jdm/libvpx,charup/https---github.com-webmproject-libvpx-,jdm/libvpx,shareefalis/libvpx,altogother/webm.libvpx,shyamalschandra/libvpx,smarter/aom,lyx2014/libvpx_c,Suvarna1488/webm.libvpx,matanbs/vp982,liqianggao/libvpx,Topopiccione/libvpx,Maria1099/webm.libvpx,mbebenita/aom,gshORTON/webm.libvpx,ittiamvpx/libvpx-1,kalli123/webm.libvpx,webmproject/libvpx,GrokImageCompression/aom,Topopiccione/libvpx,GrokImageCompression/aom,GrokImageCompression/aom,pcwalton/libvpx,openpeer/libvpx_new,Maria1099/webm.libvpx,Maria1099/webm.libvpx,matanbs/webm.libvpx,Distrotech/libvpx,Laknot/libvpx,stewnorriss/libvpx,kleopatra999/webm.libvpx,ShiftMediaProject/libvpx,Acidburn0zzz/webm.libvpx,mbebenita/aom,stewnorriss/libvpx,pcwalton/libvpx,ittiamvpx/libvpx-1,jmvalin/aom,matanbs/vp982,kleopatra999/webm.libvpx,running770/libvpx,liqianggao/libvpx,mwgoldsmith/vpx,Suvarna1488/webm.libvpx,n4t/libvpx,thdav/aom,lyx2014/libvpx_c,liqianggao/libvpx,VTCSecureLLC/libvpx,charup/https---github.com-webmproject-libvpx-,shyamalschandra/libvpx,kalli123/webm.libvpx,hsueceumd/test_hui,gshORTON/webm.libvpx,kalli123/webm.libvpx,mwgoldsmith/libvpx,GrokImageCompression/aom,kim42083/webm.libvpx,lyx2014/libvpx_c,running770/libvpx,kim42083/webm.libvpx,ittiamvpx/libvpx-1,mwgoldsmith/vpx,thdav/aom,reimaginemedia/webm.libvpx,mwgoldsmith/vpx,Acid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