libbinder_ndk: ABBinder objects are tagged.

This allows us to always cast an object directly to the underlying
object rather than temporarily putting it behind a proxy. This also
simplifies the AIBinder_associateClass API greatly.

As a side-effect, this also fixes reading null parcelables from
binder buffers due to a previously missing check.

Bug: 111445392
Test: runtests.sh
Change-Id: I0c9a75132f9da35a2500b1e83f218b180b2dda36
diff --git a/libs/binder/ndk/test/iface.cpp b/libs/binder/ndk/test/iface.cpp
index eed09f0..1317a74 100644
--- a/libs/binder/ndk/test/iface.cpp
+++ b/libs/binder/ndk/test/iface.cpp
@@ -118,12 +118,15 @@
 
 sp<IFoo> IFoo::getService(const char* instance) {
     AIBinder* binder = AServiceManager_getService(instance); // maybe nullptr
-    AIBinder_associateClass(&binder, IFoo::kClass);
-
     if (binder == nullptr) {
         return nullptr;
     }
 
+    if (!AIBinder_associateClass(binder, IFoo::kClass)) {
+        AIBinder_decStrong(binder);
+        return nullptr;
+    }
+
     if (AIBinder_isRemote(binder)) {
         sp<IFoo> ret = new BpFoo(binder); // takes ownership of binder
         return ret;