Add NDK version of MediaMuxer

and add some constness here and there.

Change-Id: Ib3caa8310691e8f27aaa1afcfaec0b384513d4f1
diff --git a/media/ndk/Android.mk b/media/ndk/Android.mk
index 82fb970..b8dd19e 100644
--- a/media/ndk/Android.mk
+++ b/media/ndk/Android.mk
@@ -24,6 +24,7 @@
                   NdkMediaCodec.cpp                     \
                   NdkMediaExtractor.cpp                 \
                   NdkMediaFormat.cpp                    \
+                  NdkMediaMuxer.cpp                     \
 
 LOCAL_MODULE:= libmediandk