Add native C APIs for working with the Asset Manager

Change-Id: I493b142c4b35e5cc1a1e85283bb5dfb306a6d261
diff --git a/native/android/Android.mk b/native/android/Android.mk
index 2fe0679..950a1e9 100644
--- a/native/android/Android.mk
+++ b/native/android/Android.mk
@@ -6,6 +6,7 @@
 # our source files
 #
 LOCAL_SRC_FILES:= \
+    asset_manager.cpp \
     input.cpp \
     looper.cpp \
     native_activity.cpp \