Add support for @nullable annotation

Using this annotation will now cause C++ types to be wrapped in
unique_ptr, and by extension be capable of handling null values.

Support extends to all arrays, Strings, Lists, and Parcelables.

Change-Id: I148a3666279c2badcba097b8925e55f8fcecb9c2
Test: Unit tests pass
Bug: 25969194
Signed-off-by: Casey Dahlin <sadmac@google.com>
diff --git a/Android.mk b/Android.mk
index f22b381..1db441a 100644
--- a/Android.mk
+++ b/Android.mk
@@ -164,6 +164,7 @@
     tests/aidl_test_client.cpp \
     tests/aidl_test_client_file_descriptors.cpp \
     tests/aidl_test_client_parcelables.cpp \
+    tests/aidl_test_client_nullables.cpp \
     tests/aidl_test_client_primitives.cpp \
     tests/aidl_test_client_service_exceptions.cpp
 include $(BUILD_EXECUTABLE)