Various improvements to nuplayer playback

- Drastically cut down the number of times we supply the AudioSink with data
by estimating the time until the sink would run out of data and then scheduling
a refill in advance of that.

- Use a dedicated looper for video decoders since they are currently taking
too long to return from OMX_FillThisBuffer (bug 5325201)

- Revise thread priorities for the OMX dispatcher and software codecs, instead
of running them at ANDROID_PRIORITY_AUDIO, they now only run at
ANDROID_PRIORITY_FOREGROUND

- Since threads created by pthread_create inherit all of the parent threads
attributes including thread priority, briefly reset thread priority to
ANDROID_PRIORITY_FOREGROUND before instantiating OMX components and then
restore it.

Change-Id: If9332a3a20dad5485333d68c11de0d2d5d3fffc3
diff --git a/media/libmediaplayerservice/nuplayer/NuPlayer.h b/media/libmediaplayerservice/nuplayer/NuPlayer.h
index cf9185b..41e015b 100644
--- a/media/libmediaplayerservice/nuplayer/NuPlayer.h
+++ b/media/libmediaplayerservice/nuplayer/NuPlayer.h
@@ -70,19 +70,19 @@
     struct StreamingSource;
 
     enum {
-        kWhatSetDataSource,
-        kWhatSetVideoNativeWindow,
-        kWhatSetAudioSink,
-        kWhatMoreDataQueued,
-        kWhatStart,
-        kWhatScanSources,
-        kWhatVideoNotify,
-        kWhatAudioNotify,
-        kWhatRendererNotify,
-        kWhatReset,
-        kWhatSeek,
-        kWhatPause,
-        kWhatResume,
+        kWhatSetDataSource              = '=DaS',
+        kWhatSetVideoNativeWindow       = '=NaW',
+        kWhatSetAudioSink               = '=AuS',
+        kWhatMoreDataQueued             = 'more',
+        kWhatStart                      = 'strt',
+        kWhatScanSources                = 'scan',
+        kWhatVideoNotify                = 'vidN',
+        kWhatAudioNotify                = 'audN',
+        kWhatRendererNotify             = 'renN',
+        kWhatReset                      = 'rset',
+        kWhatSeek                       = 'seek',
+        kWhatPause                      = 'paus',
+        kWhatResume                     = 'rsme',
     };
 
     wp<NuPlayerDriver> mDriver;