Increase the prefetcher's low water mark so it restarts fetching data earlier.

720p high bitrate content pretty much requires this.

Change-Id: I2cb29d1fa2e3c511f1b88a106a02c53c68a10f2f
diff --git a/media/libstagefright/include/NuCachedSource2.h b/media/libstagefright/include/NuCachedSource2.h
index 8cd7d4b..8cec1b1 100644
--- a/media/libstagefright/include/NuCachedSource2.h
+++ b/media/libstagefright/include/NuCachedSource2.h
@@ -58,7 +58,7 @@
     enum {
         kPageSize            = 65536,
         kHighWaterThreshold  = 5 * 1024 * 1024,
-        kLowWaterThreshold   = 512 * 1024,
+        kLowWaterThreshold   = 1024 * 1024,
 
         // Read data after a 15 sec timeout whether we're actively
         // fetching or not.