Make real API for native code to get its window.

Added implementation to use ANativeWindow and provide
it to a NativeActivity.

Change-Id: I890d71b6e15d4af71e6cf81b327961d7061ec1c2
diff --git a/native/android/Android.mk b/native/android/Android.mk
index 8c621b6..fe8ed00 100644
--- a/native/android/Android.mk
+++ b/native/android/Android.mk
@@ -7,7 +7,8 @@
 #
 LOCAL_SRC_FILES:= \
     activity.cpp \
-    input.cpp
+    input.cpp \
+    native_window.cpp
 
 LOCAL_SHARED_LIBRARIES := \
     libandroid_runtime \